Question

Given that a = 10,

Answer 1

Since $a = 10$ and $b = 2x + 5$, we have

$ab=10(2x+5)=20x+50$

So, the equation becomes

$ab = 6x^2 +11x-10 \iff 20x+50= 6x^2 +11x-10 \iff 6x^2-9x-60=0$

The solutions to this equation are 4 and -5/2, so I'm afraid there's a typo in your question.