Answer: Medium= 24 inches by 9 inches.
Large = 32 inches by 12 inches.
Step-by-step explanation: Given an artist drew a painting with proportional rectangles with the whole number dimensions in inches.
Dimensions of small rectangle: 8 inches by 3 inches.
One dimension of medium rectangle is 9 inches.
Let us assume other dimension of the medium rectangle is x inches.
Therefore, we could setup a proportion:

On cross multiplying, we get
3x = 8×9
3x = 72.
Dividing both sides by 3, we get
3x/3 = 72/3
x = 24.
Therefore, Medium= 24 inches by 9 inches.
One dimension of large rectangle is 32 inches.
Let us assume other dimension of the medium rectangle is y inches.
Therefore, we could setup a proportion:

On cross multiplying, we get
8y = 32×3
8y = 96.
Dividing both sides by 8, we get
8y/8 = 96/8.
y = 12.
Therefore, Large = 32 inches by 12 inches.