Answer:
7
Explanation:
When you match the form
... ax² + bx + c = 0
to the equation
... 3x² + 5x + 7 = 0
it is reasonable to conclude that ...
... a = 3, b = 5, c = 7.
_____
The question presumes you are familiar with the form
... ax² +bx +c = 0
which is often used as the representation of a general quadratic equation. This lets us use a, b, and c instead of specific numbers, to talk about ways of factoring, graphing, or solving equations like this.