The formula for this is an exponential formula written as:
Amount = Start value x (1-reate of change)^time
Since both sides are the same length we only need to use one side as the start value:
Start value is 10 inches
The rate of change would be 75% = 0.75
The amount of time is 5 ( reduced 5 times)
Now we have: 10 * 0.75^5
The new dimension of the picture is 2.4 inches by 2.4 inches