
Let's called the input 'z'
When we plug 'z' in the function we get ;

And we know that, this is equal to 19, so ;

Let's rearrange the equation.

So we have a quadratic equation here.
We'll use this formula to solve it :

The formula is used in equation formed like this :

In our equation,
a=2 , b=3 and c=-14
Let's plug in the values in the formula to solve,

So,

So the input can be both, 2 and