Calculation of Interest Rate:
To find the interest rate, we need to use the formula:
Simple Interest = (Principal x Rate x Time)/100

Step 1: Calculation of Principal Amount:
From the given question, we know that the sum of money amounts to 6300 in 2 years. Therefore, we can calculate the principal amount using the formula:
Simple Interest = (Principal x Rate x Time)/100
6300 = (Principal x Rate x 2)/100

Solving for Principal, we get:
Principal = (6300 x 100)/(Rate x 2)

Step 2: Calculation of Interest:
Now, we can find the interest earned in 1 year by using the formula:
Interest = (Principal x Rate x Time)/100
Interest = (Principal x Rate x 1)/100

Step 3: Calculation of Rate:
Next, we can calculate the rate of interest by using the formula:
Rate = (100 x Interest)/(Principal x Time)
Rate = (100 x Interest)/(Principal x 1)

Step 4: Calculation of Final Amount:
Now, we can calculate the final amount after 3 years and 9 months using the formula:
Final Amount = Principal + Interest
Final Amount = Principal + (Principal x Rate x 3.75)/100

Step 5: Calculation of Principal:
Using the above formula, we can find the value of Principal, which is common in both equations.
7875 = (Principal x Rate x 3)/100 + (Principal x Rate x 3.75)/100

Solving for Principal, we get:
Principal = 4500

Step 6: Calculation of Rate:
Using the value of Principal in Step 1, we can now calculate the rate of interest:
6300 = (4500 x Rate x 2)/100
Rate = 7%

Therefore, the interest rate is 7%.

4500??