Question 934113
x hours done at 85 per hour, y hours done at 80 per hour.


{{{system(80x+85y=2100,x+y=25)}}}


Divide members of the money equation by 5:


{{{system(8x+9y=420,x+y=25)}}};
Better now?  
Solve the system; Elimination Method may be a good way to start.