Question

if 18 inches is equal to 1 1/2 feet, how many feet long is a 36 inch board? A 72 inch board? A 144 inch board?

Answer 1

18 inches=  1 1/2 feet= 1.5 feet

18 inches = 1.5 feet

(1) Now we make a proportion to find feet for given inches

$\frac{feet}{inches} = \frac{feet}{inches}$

$\frac{1.5}{18} = \frac{x}{36}$

1.5 * 36 = 18*x

54 = 18 x (Divide by 18 on both sides)

x = 3

3 feet long is a 36 inch board

(2) 72 inch board

$\frac{1.5}{18} = \frac{x}{72}$

1.5 * 72 = 18*x

108 = 18 x (Divide by 18 on both sides)

x = 6

6 feet long is a 72 inch board

(3) 144 inch board

$\frac{1.5}{18} = \frac{x}{144}$

1.5 * 144 = 18*x

216 = 18 x (Divide by 18 on both sides)

x = 12

12 feet long is a 144 inch board

Answer 2

3, 6, and 12.
18 times 2 is 36 so 1 1/2 times 2 is 3
18 times 4 is 72 so 1 1/2 times 4 is 6
18 times 8 is 144 so 1 1/2 times 8 is 12