Combine Leverage:
Combine leverage refers to the combined effect of operating leverage and financial leverage on a company's earnings before interest and taxes (EBIT) and earnings before taxes (EBT). It measures the sensitivity of a company's profitability to changes in sales.

Operating Leverage:
Operating leverage is a measure of how fixed costs and variable costs contribute to a company's overall cost structure. It quantifies the relationship between sales revenue and EBIT.

Operating leverage can be calculated using the following formula:
Operating Leverage = Contribution Margin / EBIT

Contribution margin is calculated as:
Contribution Margin = Sales - Variable Costs

In this case, the sales are $400,000 and the variable costs are 80% of sales, which amounts to $320,000. Thus, the contribution margin is $80,000.

Operating Leverage = $80,000 / EBIT

Financial Leverage:
Financial leverage measures the impact of a company's debt on its profitability. It quantifies the relationship between EBIT and EBT.

Financial leverage can be calculated using the following formula:
Financial Leverage = EBIT / EBT

In this case, the interest expense is $100,000. Therefore, the EBT is calculated as:
EBT = EBIT - Interest Expense
EBT = EBIT - $100,000

Financial Leverage = EBIT / (EBIT - $100,000)

Combined Leverage:
Combined leverage is the product of operating leverage and financial leverage. It measures the overall effect of both types of leverage on a company's profitability.

Combined Leverage = Operating Leverage * Financial Leverage

Effect of 10% Increase in Sales on EBIT and EBT:
To determine the effect of a 10% increase in sales on EBIT and EBT, we can use the calculated values of operating leverage and financial leverage.

Since operating leverage is calculated as the contribution margin divided by EBIT, a 10% increase in sales will result in a 10% increase in the contribution margin, assuming all other costs remain constant. Therefore, the new contribution margin will be $88,000 ($80,000 * 1.1).

To calculate the new EBIT, we can use the formula:
EBIT = Contribution Margin - Fixed Costs
EBIT = $88,000 - $300,000
EBIT = -$212,000

Since financial leverage is calculated as EBIT divided by EBT, the 10% increase in sales will also result in a 10% increase in EBIT. Therefore, the new EBIT will be -$212,000 * 1.1 = -$233,200.

To calculate the new EBT, we can substitute the new EBIT value into the EBT formula:
EBT = EBIT - Interest Expense
EBT = -$233,200 - $100,000
EBT = -$333,200

In summary, a 10% increase in sales will result in a negative EBIT of -$212,000 and a negative EBT of -$333,200. This indicates that the company will incur losses even with the increase in sales.