Emily, I was confused by algebra the first time I took it. Let's see if we can help.
When we think of a function, we are trying to figure out what our y-coordinate is when we use different x-values. The y-value is dependent on what the x-value is. The amount of spaghetti sauce I can make could be my y, and the number of tomatoes I have could be my x. Get it?
We usually put y first, so a function looks like y = something to do with x. It can also look like f(x) = something to do with x.
Our x-value is the week number. Every week, he gets $10, so after week 3, he has $10(3), right? This we call 13x.
If he starts with $13, this would look like 13 + 10x. So far, so good?
Remember, though, I said y goes first. Whatever goes with x is next, then our constant.
y = 10x + 13
At the beginning of week 7...
y = 10(7) + 13
y = 70 + 13
y = 83
Hope this helps!
