To make q subject of the formula
a(q-c)=d

A(q-c)=d
a(q-c)/a=d
(q-c)=d/a
(q-c+c)=d/a+c
q=d/a+c

Explanation
a is multiplying everything in the bracket, so to get it on the other side of the equation, you multiply, the ‘a’ is dividing the ‘d’ because anything that is done on one side should be done on the other
‘c’ is being subtracted from ‘q’ so we do the opposite which is addition in order to cancel them out and get the ‘q’ by itself