Answer:
One possible equation is 2m+16 = 40
There are other possible equations to set up as well.
That equation solves to m = 12 which means both plans cost the same when you go 12 MB over the limit (using 27 MB total).
===============================================================
Explanation:
The unlimited plan costs $40 a month no matter how much data you use.
The second plan costs $16 a month, and there are no extra fees as long as you don't go over the limit of 15 MB. If you do exceed this limit, then you're charged an extra $2 per MB. That means an extra 2m dollars is tacked onto the 16 mentioned earlier, where m is the amount of MB you've gone over the limit. Overall, the expression 2m+16 represents the cost of the second plan. If you don't go over the limit, then you'll use m = 0 for the second plan.
Set that expression equal to 40 to set up the equation. Solving the equation leads to...
2m+16 = 40
2m = 40-16
2m = 24
m = 24/2
m = 12
If you exceed the limit by 12 MB, then both plans cost the same at $40 per month.
Note: Going 12 MB over the limit means you've used 15+12 = 27 MB.
