3. (a) A father is 28 years older than the son. In 5 years the father's age will be 7 years more than twice that of the son. Find their present age.

Step 1 ：Let the father's age be F and the son's age be S. We have two equations:

Step 2 ：$F=S+28$

Step 3 ：$F+5=2(S+5)+7$

Step 4 ：Solve the system of equations:

Step 5 ：Substitute the first equation into the second equation:

Step 6 ：$(S+28)+5=2(S+5)+7$

Step 7 ：Simplify the equation:

Step 8 ：$S+33=2S+17$

Step 9 ：Isolate S:

Step 10 ：$S=16$

Step 11 ：Substitute the value of S back into the first equation:

Step 12 ：$F=16+28$

Step 13 ：$F=44$

Step 14 ：$\boxed{{\displaystyle \text{The father's present age is 44 years old, and the son's present age is 16 years old.}}}$