Given the information on the problem, we can write the following expression to represent the cost of hirigin Carpenter 4 U:

where 'y' is the total cost and 'x' is the number of hours.
next, we know that the slope-intercept equation of the line is:

then, in this case, the slope is m = 45 and the y-intercept is b = 50
Finally, if we decided to hire Carpenter 4U for 20 hours, then we have to make x = 20 and solve for y:

therefore, it will cost $950 for 20 hours of work