Direct varition and proportion ? PLease help as possible?

Question

A carpet company charges $ 450 to lay carpet on a floor whose area is 200 square feet.

A.) How much would the company charge to lay carpet on a floor whose area is 280 square feet?

Answer 1

$450/200 = x/280
9/4 = x/280
9/1 = x/70
x = $630

I did it that way to avoid having to multiply big numbers, and then divide by another big number.