An algebra problem

I did it by thinking practically For example i supposed 3 ages of son - 5,10,15 1)- 5*4=20, after 30year =5+30= son's age and 20+30= 50 father's age. 50/2=25. Hence it is wrong. Do same with other three no. And u will get that 15 fit in this situation, consequently 15 son's age is ryt and therefore father age would be 60.

I am not good at maths but my approach to question is always practical most of the tym.

$S=\dfrac{F}{4}$ $\implies$ $\color{#D61F06}\boxed{1}$

$S+30=\dfrac{1}{2}(F+30)$

$2S+60=F+30$ $\implies$ $\color{#D61F06}\boxed{2}$

Substitute $\color{#D61F06}\boxed{1}$ in $\color{#D61F06}\boxed{2}$ .

$2\left(\dfrac{F}{4}\right)+60=F+30$

$30=\dfrac{1}{2}F$

$\color{#3D99F6}\boxed{F=60}$

Suppose, the age of son is x . so the age of father is 4x . so the equation is,4x+30=2(x+30) or, 4x+30= 2x+60 or, 4x-2x= 60-30 or, 2x= 30 or, x= 15 So, the age of father is 4.15 =60