Question

28/21 = 42/x solve for x

Answer 1

28/21=42/x   multiply both sides by x

28/21x=42   divide by 28/21 on both sides ( or multiply both sides by 21/28)

X= 63/2
X= 31 1/2

Answer 2

28/21 = 42/x

Cross Multiply

28*x = 21*42

x = 21*42/28      use your calculator.

x = 31.5

x = 31  1/2

option C

Hope this explains it.