She'll need 30 lemons for 10 cups of water. Just multiply 3 by 10, or you can add 3 to every cup of water.
My answer is short, but hopefully I helped.
Most textbooks interpret standard form of a quadratic function to be as follows:
f(x) =

In the function f(x) =

, notice we do not have a value for "c". Just place a "0" in for the c and you have standard form.
the criteria for standard form:
1. All like terms are combined
2. Degree must drop from left to right
3. The leading coefficient cannot be equal to zero.