Let "x" be the charge for manicures and let "y" be the charge for pedicures.
We can write the following system:
[tex]\begin{gathered} 31x+17y=955 \\ 21x+39y=1389 \end{gathered}[/tex]
We're going to solve this system with the substitution method.
For this, we're going to solve the first equation for y:
[tex]\begin{gathered} 17y=955-31x \\ y=\frac{955-31x}{17} \end{gathered}[/tex]
And now, we're going to replace this expression for y in the second equation to solve a linear equation which is easier:
[tex]\begin{gathered} 21x+39y=1389 \\ 21x+39(\frac{955-31x}{17})=1389 \end{gathered}[/tex]
Now, solving, we got:
[tex]\begin{gathered} 21x+39(\frac{955-31x}{17})=1389 \\ \\ 21x+\frac{37245}{17}-\frac{1209}{17}x=1389 \end{gathered}[/tex]
We could multiply the whole equation by 17 to make the process easier:
[tex]\begin{gathered} 357x+37245-1209x=23613 \\ -852x=-13632 \\ x=16 \end{gathered}[/tex]
Therefore, x=16, so the charge for manicures is $16.
We're going to replace this value in any of both equations so we could find the value of y (The charge for pedicures)
[tex]\begin{gathered} 31(16)+17y=955 \\ 17y=955-496 \\ 17y=459 \\ y=27 \end{gathered}[/tex]
Therefore, y=16, so the charge for pedicures is $27.