we are given that the cost of t-shirts follows a linear relationship. If "x" is the number of t-shirts then the total cost must be equal to:

Since the cost of 30 shirts is $175, that means that we have the following point:

Replacing the point in the equation we get:

Solving the operations:

Solving for "b" by subtracting 150 to both sides:

Replacing we get:
