Let h be the hours and y the total charge. Then, for Happy Paws, we have
and for Woof Watches, we have
Then, we need to solve these equations.
Solving by elimination method.
If we multiply by -1 the first equation, we have the equivalent system of equations:
If we add both equations, we obtain
because y-y=0. Then, it yields,
If we move -9 to the left hand side as -9, we have
Hence, to find the total cost, we must substitute this values into one of the 2 equations. If we choose the first one, we obtain
Then, the answers are:
The equation is
and, the total cost of the services will be equal at 7.2 hours