we have

Step 
<u>Clear the variable y</u>

Adds
both sides


Step 
<u>Convert in function notation</u>
Let


therefore
<u>the answer is</u>

Nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
Let dan's age be x then:-
james age is 3x and 2(x + 3x) is Pauls age so we have:-
x + 3x + 2*4x = 120
12x = 120
x = 10
so Dans age is 10 , James's age is 30 and Paul's age = 80