What is the specific heat of a substance if 2100 J is required to raise a 312 g sample by 15 degrees Celsius?

Question

So I use the q = mcΔT formula
2100J = (312 g)c(85 °C - 15 °C)
I'm not sure if I did it right.

Answer 1

I don't know where you obtained the 85 C?
m = 312, right
c = unknown, right
The problem tells you delta T is 15, where did the 85 come from?

Answer 2

To be honest, I thought you suppose to subtract everything from 100. I'm being dumb. I don't know where I get 85 from. Forget that. So, how do I solve this problem?