The cost of renting the mower for 3 hours is $16.
Formula:
[tex]c=4+4h[/tex]Where:
c= total cost in dollars
h= number of hours the mower is rented.
So, we simply have to substitute h=3 ( mower rented for 3 hours) and solve:
[tex]c=4+4(3)[/tex][tex]c=4+12[/tex][tex]c=16[/tex]