Answer
Assistant: 35 hours
Plumber: 70 hours
Work Step by Step
They charge 25 for an hour of assistants work and 45 for plumbers equivalent. Assistant worked certain amount of hours (x) and plumber twice as much (2x). The charge on the final bill was 4025.
45$\times$2x+25x=4025
90x+25x=4025
115x=4025
x=35
And plumber did twice as much so 2$\times $35=70 hours
