Question 725565
Solution:

Given : A - B = 3 ------------eq.1
        D = 2A    ------------eq.2
        B = 2C or C = B/2 ----eq.3
        D - C = 30 -----------eq.4

Put eq.2 , eq.3 in eq.4, we get

2A - B/2 = 30

4A - B = 60 ------------------eq.5

Solving eq.1 and 5, we get,

A = 19
B = 16