a=7
you would start with the equation 3a+4=a+18
to solve you try to get a by itself. you would first subtract an a from each side to get all the a's together- 2a+4=18
then you would subtract 4 from each side to get the 2a by itself- 2a=14
finally to get a by itself you divide each side by 2, to get a=7
