Given:
A business owner wants to have the front window of her store painted and is considering two artists for the job.
First, Lena has quoted a flat rate of $191 for the job.
so, y = 191
Second, Cara's quote is $20 per hour, plus $31 to cover the cost of materials.
So, y = 20x + 31
where x is the number of hours
so, we have the following system of equations:

solve using substitution,
so substitute with (y) from equation (1) into equation (2)

Solve the equation to find (x)

so, the answer will be:
The number of hours = 8 hours
and the cost will be $191