To solve this problem we have to write an equation for each condition where the first charge is x and the second charge is y so:
For the total hours will be:
[tex]x+y=25[/tex]and the total charge will be:
[tex]65x+100y=2150[/tex]We can solve the first equation for x so:
[tex]x=25-y[/tex]and we replace that in the secon equation so:
[tex]65(25-y)+100y=2150[/tex]and we solve for y so:
[tex]\begin{gathered} 1625-65+100y=2150 \\ 35y=2150-1625 \\ y=\frac{525}{35} \\ y=15 \end{gathered}[/tex]And with this value of y we can find x so:
[tex]\begin{gathered} x=25-15 \\ x=10 \end{gathered}[/tex]