The correct response is:
C It is linear because it increases at a constant rate.
The function \( y = 15x \) is a linear function since it can be represented in the form \( y = mx + b \) where \( m \) is the slope (15 in this case) and \( b \) is the y-intercept (0 in this case). The function increases at a constant rate of 15, meaning for every additional hour \( x \) worked, Sarah earns an additional $15.