College algebra
posted by Lee .
a company finds it can produce 15 heaters for $4300, while producing 20 heaters costs $5500. Express y, as a linear function of the number of heaters, y. Determine the cost to produce 30 heaters.
y = _________
Cost to produce 30 heaters $_________
Help I'm not sure how to solve this problem. Thank you

y=mx+b
4300=m*15+b
5500=m*20+b
subtract the first from the second
1200=5m
m= you solve it. THen put it in either equation, and solve for b. 
Thank you so much. I can't believe it was so simple..:):)