Saving Calculation:
To calculate saving, we need to use the formula:

Saving = Disposable Income - Consumption

Disposable Income:
Given that 5 = (-)100, we can deduce that the disposable income is 5.

Consumption:
To calculate consumption, we need to use the formula:

Consumption = Disposable Income - Saving

Let's substitute the values that we have:

Consumption = 5 - Saving

Marginal Propensity to Save:
The marginal propensity to save (MPS) is the proportion of additional income that is saved rather than consumed. It represents the change in saving with respect to a change in income.

Given that the marginal propensity to save (MPS) is 0.4, this means that for every additional unit of income, 40% of it is saved.

Calculating Saving:
To calculate saving, we can rearrange the consumption formula:

Saving = Disposable Income - Consumption

Since Consumption = Disposable Income - Saving, we can substitute it in the above equation:

Saving = Disposable Income - (Disposable Income - Saving)

Simplifying the equation:

Saving = Disposable Income - Disposable Income + Saving

Combining like terms:

2 * Saving = Disposable Income

Dividing both sides by 2:

Saving = Disposable Income / 2

Substituting the value of disposable income:

Saving = 5 / 2

Calculating the value:

Saving = 2.5

Conclusion:
The saving is 2.5 when disposable income is 5 and the marginal propensity to save is 0.4.