x=number of boys in the club at first
y=number of girls in the club at first.
(x+y) = members were in the club at first.
We can suggest the next system of equation.
x/y=1/2 ⇒ x=y/2
(x+5)/y=3/4 ⇒4(x+5)=3y
Finally, we have the next system of equations:
x=y/2
4(x+5)=3y
We are going to solve by substitution method.
4(y/2 + 5)=3y
2y+20=3y
2y-3y=-20
-y=-20
y=20
x=y/2
x=20/2
x=10
(x+y)=10+20=30
Answer: There were 30 members int the club at first, they were 10 boys and 20 girls.
