So, your equation you have is y = 5x + 253.
They want to know how many total pieces you will have to put together after 45 more minutes.
So, you'll want to insert 45 in for x in the equation. Like so:
y = 5(45) + 253
Now you solve:
y = 225 + 253
y = 478
So this means you will have 478 pieces put together after another 45 minutes. There are 2573 pieces total, yes?
So, you do 2573-478
This equals = 2,095
So this means you'll still have 2,095 pieces to put together. Whew!