D over dx (x sin^2(x)) = sin(x) (sin(x) + 2 x cos(x))
now why would you put a test like this out here
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.