Hi there.
I'm just going to put the answer for now. I might come back and edit my answer if I figure out how to solve this the long way.
All I did was figure out what exponent you raise 10 to.
10³ = 1000
So, we now have 8 + 10³ = 1008
Edit:
I did it on paper - here it is broken down.
8 +

= 1008
Subtract 8 from both sides.

= 1000
We know that 10³ = 1000
<em>x</em> = 3
~
The signs of the x-term and the constant term are both positive, so the signs of the constants in the binomial factors must be the same and must both be positive. The only offering that meets that requirement is
... C (2x+1)(3x+5)
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If you multiply that out, you get 6x² + 10x + 3x + 5 = 6x² +13x +5, as required.
The sign of the constant term is the product of the signs of the constants in the binomial factors: (+1)·(+5). We want a positive sign for the constant, so both binomial factor constants must have the same sign.
When the signs of the binomial factor constants are the same, the x-term constant will match them. Thus, for a positive x-term constant, both binomial factor constants must be positive.