যদি P :Q : R, 1/3 : 2/3 : 1/4 হয় এবং Q = 56 হয়, তাহলে P - R = কত?

Multiply by 12: P : Q : R = 4 : 8 : 3. Q = 56 means one part = 7, so P = 28 and R = 21, and P − R = 7.