Since 1 ft=12im, then 33ft=396in. Hence, 33ft 9in = 405 inches.
Using the ratio, let the prices be 3x,5x, and 7x, all in inches.

So, we can write and solve for x: 3x+5x+7x=405

15x=405

x=27

So, the lengths of P,Q and R are: \(\displaystyle{P}\to{3}{\left({27}\right)}={81}\) inches or 6 ft 9in

\(\displaystyle{Q}\to{5}{\left({27}\right)}={135}\) inches or 11 ft 3 in

\(\displaystyle{R}\to{7}{\left({27}\right)}={189}\)inches or 15 ft 9 in

So, we can write and solve for x: 3x+5x+7x=405

15x=405

x=27

So, the lengths of P,Q and R are: \(\displaystyle{P}\to{3}{\left({27}\right)}={81}\) inches or 6 ft 9in

\(\displaystyle{Q}\to{5}{\left({27}\right)}={135}\) inches or 11 ft 3 in

\(\displaystyle{R}\to{7}{\left({27}\right)}={189}\)inches or 15 ft 9 in