The equation system is:
[tex]\begin{gathered} S+0.5=J \\ 7S+7J=112 \end{gathered}[/tex]Where S = Susan's salary per hour; J = Janet's salary per hour. The second equation means the combined income for 7 worked hours.
One substitute first equation into the second and solve for S:
[tex]\begin{gathered} 7S+7(S+0.5)=112 \\ 7S+7S+3.5=112 \\ 14S=108.5 \\ S=7.75 \end{gathered}[/tex]Then, we use the obtained value S to get Janet's salary:
[tex]\begin{gathered} S+0.5=J \\ 7.75+0.5=J \\ J=8.25 \end{gathered}[/tex]Answer a) Susan's salary = $7.75; Janet's salary = $8.25
Answer b)
[tex]7S+7\mleft(S+0.5\mright)=112[/tex]