direct variation

Question

if y = 12 when x =3 , find y when x = 7.

Answer 1

y is direct variation to x  then y = kx

Given numbers form a ratio expressed as y/x = 12/3

To find y when x = 7

We set up another ratio is y/7.

By the definition both ratios are equal 12/3 = y/7

4 = y/7

Multiple to each side by 7.

4*7 = 7y/7

y = 28