How do i solve for x (ax+bx)/3=c in terms of a and b and c

Already in terms of c x(ax+bx)/3=c
(ax^2 + bx^2)/3=c. Multiply parentheses by x
ax^2 + bx^2=3c. Multiply each side by 3
ax+bx=√3c. Take the square root of both sides
x(a+b)=√3c
a+b=√3c/x
a=√3c/x - b or b=√3c/x - a

Where’s the problems ? ?