When Am I Ever Going To Use y=mx+b????

As a part of my volunteer job with CAS, I tutor a couple of foster kids and I have been for the past year. Every week I visit them and tutor them in mainly math, but in other subjects as well.
I now have 15 students, 13 of which I am paid as a private tutor and the 2 foster kids I mentioned.

My students are from grade 1 through 11 and all of them have trouble with/need a little extra help in math.

One of my grade 11 students and I were working on her math homework one day and she grew frustrated after a few questions.
She asked me when in "the hell" is she ever going to use "y=mx+b" (linear equation... for those that don't know, it's the equation you learn through high school ... the unit where you find midpoints of a line, the x and y intercepts etc... Have I lost you?).

Anyway, I get what she is saying. We don't always use all of what we learned in math. You may think math was pointless because the field you are in now career-wise depends on everything but linear and quadratic equations.

But what she didn't seem to understand was that what she is studying in math now is just a more advanced level of all of her accumulated knowledge in math over the years.

She is able to learn now because she has the knowledge of the basic concepts she has learned since the first grade. She has little interest in this fact. She has more interest in how much money I make tutoring because she sees her mom pay me every week. She also knows I tutor her neighbours and friends and have 15 students. She knows I get paid cash. She can add cash and coins VERY quickly. She's 16, and to her, seen cash is a big deal.

I asked her then, what was the point of her reading Charlotte's Web back in elementary school? Is she ever going to live as a pig and have a spider friend? Of course, being a 16 year old, she rolled her eyes and carried on doodling in the margins of her lined paper.

She then looked at me with a grin like she has an advantage in our little debate and said, "You work in a daycare right? And a group home? When was the last time YOOOOU used y=mx+b?"

Me: "Today".