Greta had $2,992 in a savings account with simple interest. She had opened the account with $2,200 exactly 4 years earlier. What was the interest rate? Use the formula i = prt, where i is the interest earned, p is the principal (starting amount), r is the interest rate expressed as a decimal, and t is the time in years.

18.3824%

Step-by-step explanation:

Sorry, this may be wrong. I am using an old skill, so it may be wrong.

The vertex form of a quadratic function:
(h,k) - the coordinates of the vertex 

If a>0, then the parabola opens upwards, so the vertex is the minimum of the function.
If a<0, then the parabola opens downwards, so the vertex is the maximum of the function.

a=-1<0
the vertex is maximum

a=1>0
the vertex is minimum