systems of equations

Question

you want to buy a cellphone and must first do some research on which cell phone provider has the best  plan.  at2 charges a flat rate of $3plus 2 cents per minute. pabell charges a $8.50 flat rate plus 1 cent per minute.

write the equation for both at2 and pabell

Answer 1

at2: c=3+0.02t; pabell: c=8.50+0.01t, where c=cost in dollars and t=time in minutes.

[The two plans have equal cost ($14) when 3+0.02t=8.50+0.01t; 0.01t=5.50; t=550 minutes. Below that time at2 is cheaper and above pabell is cheaper.]