Question

After how many hours does he break even?

Answer 1

25+30x=5x²-10
5x²-30x-35=0
x²-6x-7=0    -7=-7*1, -6=-7+1
(x-7)(x+1)=0
x-7=0, x=7 hours.
x+1=0, x=-1 (we cannot take negative for hours)
So, answer is 7

Check
y=25+30*7=235
y=5x²-10= 5*7²-10=245-10 =235