Anybody got any ideas about this math word problem?

Georgio wishes to purchase a second hand iPhone, which costs $485. He has saved $60.
He can save a further $30 per month, but the price of the iPhone rises by an average $0.90 per month.

(a) Write an equation to represent the cost C, of the iPhone afterrm months.

OK. Got this part.

C = 485 + .90m

(b) Write an equation to represent the amount that Georgio has saved, S, afterrm months.

Got this part too.

S = 60 + 30m

I'm stumped by this part:

(c) How many months will it take him to save enough for the iPhone?

I have no clue how to do (c). Anybody got any idea?

Now just add $30 with $60 than keep adding $30 dollars until you reach the amount of money to pay for iPhone make sure you count how many times which are the months.

now add $0.90 with each out the exact amount of times the months are than take that away from the iPhone money Geogio saved up

than with $30 subtract $0.90 and that would equal 29.1 than add that with the rest until you reach the iPhone number

the explanation is hard to understand so:

$60 + 29.1 + 29.1 + 29.1 + 29.1 + 29.1 + 29.1 + 29.1 + 29.1 + 29.1 + 29.1 +29.1 + 29.1 + 29.1 + 29.1 + 29.1

= 15 months