You will need to show us a picture if u don’t mind kind sir
We are given a system of equations,

This will translate into a 2x2 matrix of coefficients (because 2 equations and 2 unknowns),

The matrix will then be applied to the vector (lower dimensions on top),

And the result vector will be whats on the other side of equals sign,

So to put everything together,

Hope this helps :)
It’s just y= 17x. There’s nothing added or subtracted, or else it wouldn’t be (0,0).
Divide the total amount she has by how much she needs per batch.
When dividing fractions, flip the second one over and then multiply straight across.
9/10 / 1/4 becomes: 9/10 x 4/1
9/10 x 4/1 = 36/10 = 3 6/10 = 3 3/5
She can make 3 more batches and have 3/5 of a teaspoon left over.