say your equation is y=mx+c
to solve for x you rearrange the equation to make x the subject (x=...)
to do this; you move the c to the other side;
y-c=mx becomes -c as its on the other side now
then to get x on its own
(y-c)/m=x you divide by m as it is times by on the other side
then to solve, you will normally be given values for the other components (y, m, c) so you plug in the numbers and calculate x
