Question

Two competing cell phone companies have recently restructured their payment plans. Mobilama requires a $20 activation fee and charges $25 per month for their basic plan. Ringit Wireless requires no activation fee and charges $35 per month for their basic plan. When will the two plans be equal in cost?

Answer 1

we can write these two payment plans in the form of a function
the total cost of mobilama m(x) and the total cost of ringit r(x)

m(x) = 20+25x -- start with a 20 activation fee, and every month "x" we add an additional 25

r(x) = 0 + 35x -- no activation fee, and every month "x" we add an additional 35 to the bill

Answer 2

we want to determine at what time/ how many month will the total costs of these 2 payment plans be equal to each other

so when m(x)=r(x)

thus
20+25x=35x

and then solve for x which is hte total amount of months required before both payment plans have the same total cost