Martin has a vegetable garden that is 8 feet long and 5 feet wide. Next year, Martin wants to increase both the length and width of his vegetable garden by 15%. By what percent will the area of Martin’s vegetable garden increase with these changes?
The area of Martin’s current vegetable garden is 8 * 5 = <<8*5=40>>40 square feet.
Martin wants to increase the length by 8 * 0.15 = <<8*0.15=1.2>>1.2 feet.
Martin wants to increase the width by 5 * 0.15 = <<5*0.15=0.75>>0.75 feet.
After the changes, the length of Martin’s vegetable garden will be 8 + 1.2 = <<8+1.2=9.2>>9.2 feet.
After the changes, the width of Martin’s vegetable garden will be 5 + 0.75 = <<5+0.75=5.75>>5.75 feet.
The area of Martin’s vegetable garden after the changes will be 9.2 * 5.75 = <<9.2*5.75=52.9>>52.9 square feet.
The area of Martin’s vegetable garden will increase by 52.9 - 40 = <<52.9-40=12.9>>12.9 square feet.
By what percent will the area of Martin’s vegetable garden increase? The percent increase will be (12.9 / 40) * 100% = 32.5%. Answer: \boxed{32.5}.