Tom wants to place a photograph that is 8.5 inches wide on his science fair poster. his poster board is 21.25 inches wide. how far from each edge should he place the photograph if he wants it to be centered

6 3/8 inches (6.375 inches)

Step-by-step explanation:

For simplicity we'll assume that both the photo and the poster board are square.  To determine the width of the border, subtract 8.5 inches from the poster board width 21.25 inches, obtaining 12.75 inches, and then divide that 12.75 inches by 2:  6.375 inches (6 3/8 inches).  

Set the photo 6 3/8 inches from each edge of the poster board.

b. 24 mm

step-by-step explanation:

use the pythagorean theorem.

a^2 + b^2 = c^2

a^2 + 7^2 = 25^2

a^2 + 49 = 625

a^2 = 576

a = 24

answer: b. 24 mm