t2 s4 #35 please!

*a* = 18*t* + 15

The key to correctly interpreting questions like this one is paying attention to where the variable (*t*, in this case) is. The variable will be multiplied by the number that’s added every time. The variable will *not* be attached to the starting point. You want Jane’s initial deposit here—the starting point. **That’s going to be 15**. She started by depositing $15, and then every week after that she deposits $18.

I think it’s useful to note that this is really just the slope-intercept form of a line, usually shown as *y* = *mx* + *b*. In that equation, the variable is attached to *m*, which you know is the slope, or the rate of change. Another way of thinking about this is that every time *x* increases by 1, the *y* value increases by *m*. The starting point, *b*, is the value of *y* when *x* = 0 (also known as the *y*-intercept).