t2 s4 #35 please!
a = 18t + 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).