Solve. 4/7 = 21 / x - 3

a. x = 15

b. x = 94

c. x = 39 3/4

d. x = 12 3/7

4/7 = 21 / (x-3)

Multiply x-3 on to both sides to get

4 (x-3) / 7 = 21

Multiply both sides by 7 to get

4 (x-3) = 144

Multiply to get

4x - 12 = 144

Add 12 on both sides to get

4x = 156

Divide both by 4 to get

156/4

Or

39

4/7 = 21 / (x - 3)

multiply by (x-3) on each side

4 (x-3) / 7 = 21

multiply by 7 on each side

4 (x-3) = 21*7

distribute

4x-12 = 147

add 12 to each side

4x = 159

divide by 4

x = 159/4

change back to a mixed number

4 goes into 159 39 times with 3 left over

39 3/4

Choice C