A firm pays $1.75 for each copy of a magazine and sells each one for $2.50. There is a fixed monthly cost of $40 for printing the publication. If the firm wants to make $550 dollars next month, how many magazines do they have to sell? Write and solve an equation that represents this scenario.
(2.50-1.75)M - 40 = 550
.75M = 590
M = 590/.75