3 months Let's express the amount of money spent on club A as a function of the number of months A = 21 + 26m And do the same thing for club B B = 42 + 19m We now want to set the 2 expressions equal to each other. 21 + 26m = 42 + 19m And solve for m. First subtract 21 from both sides 26m = 21 + 19m Now subtract 19m from both sides 7m = 21 And divide both sides by 7 m = 3 Therefore after three months, the total cost for each health club will be the same.