Part A:
[tex]\begin{gathered} x+y=75 \\ x+15=y \end{gathered}[/tex]
Part B:
we need to solve x, we can replace the second equation(y=x+15) on the first equation
[tex]\begin{gathered} x+(x+15)=75 \\ x+x+15=75 \\ 2x=75-15 \\ x=\frac{60}{2} \\ \\ x=30 \end{gathered}[/tex]
he spends 30 minutes jogging
Part C:
Its impossible because if he rides 60 minutes must jog 15 less minutes, 45 minutes, and the sum isnt 75
[tex]60+45=105[/tex]
