2 errors
You multiplied the right side of b) by 100 but did not do it to the left side
your equation no would be in cents, but your equation in a) is in dollars --->
mismatching units.
secondly, you forgot the x after the 850 in " r(x)-c(x) = 850 - 3x+3080 "
so:
a) c(x)= 3x+3080
r(x)= 8.50x
at break-even point c(x) = r(x)
8.50x = 3x+3080
etc