Explanation:
The equation y = 50x + 25 represents the cost of the plumber's work based on the number of hours (x) he works. To find the cost for 8 hours of work, we can substitute 8 for x in the equation. So, we have y = 50(8) + 25 = 400 + 25 = 425. So, the cost of the plumber's work for 8 hours is $425.