Lets set up an equation for this question.
We know that he makes $50 per day no matter what, this is our constant. He also makes $5 per shirt, this is what will be multiplied by out X.
So, Y = 5x + 50
This states that every day, Y, Joe will make $5 per shirt + $50 for just working.
Now, we know that his goal is $150, which is how much he wants to make every day. We can replace this for the Y in our equation, which now means we have:
150 = 5x + 50
So lets try and get x by itself, we do this by removing all numbers that are not X from the right side.
150 - 50 = 5x + 50 - 50
Remember, what we do to one side we must do to both sides.
100 / 5 = 5x / 5
20 = x
This means that Joe needs to sell 20 shirts per day to reach his goal of $150.
I hope I've helped! :)
