2.50 + 1.25x = 22 first we must get x by itself, to do this we first subtract 2.50. (what you do to one side you have to do to both sides)
2.50-2.50 +1.25x = 22-2.50
1.25x = 19.5 now you see x is being multiplied by 1.25 so to undo this you have to divide it by 1.25 and what you do to one side you have to do to the other
1.25x/1.25 = 19.5/1.25
1x = 15.6
x= 15.6