It costs $23 per hour plus a flat fee of $16 for a plumber to make a house call. what is the equation of the form y = mx + b for this situation?

So, we just need to figure out what number means what.

So, the flat fee is $16.  This is going to be charged even for "zero" hours of work.  So, this will be the Y-intercept (also known as the B-Value)

$23 per hour means that as time progresses, you will be charged more.  23 will be our slope since it's price is dependent on time spent.  The slope is also known as the M value.

So, we just plug in our numbers and get

Y = 23x + 16