Let the present ages of A, B, F and S be x, y, z and t years respectively.
A is elder to B by 2 years. Thus, we have
F is twice as old as A. Thus, we have
B is twice as old as S. Thus, we have
The ages of F and S is differing by 40 years. Thus, we have
So, we have four equations
Here x, y, z and t are unknowns. We have to find the value of x.
By using the third equation, the first equation becomes
From the fourth equation, we have
Hence, we have
Using the second equation, we have
Hence, the age of A isyears.