Explanation:
1) let's say X will be next to our 15 dollars and y next to 18 dollars
so
15x + 18y = 252
it also tells us that the weekdays is 3 times as many hours as y. In other words:
x = 3y
2) As the question asks for the number of weekend hours, let's solve for y.
Here, it's easier to just substitute x in the original equation. If you put 3y as a replacement of x, the equation becomes:
(15*3y) + 18y = 252
expand to:
45y + 18y = 252
add on
63y = 252
divide both by 13
y=4
Therefore Vincent works 4 hours on the weekend so during the weeks he works 20 hours