Question 199600
To factor the quadratic, you need to look at the factors for the coefficients of of leading term (20) and the trailing term (21). Then decide which pairs of factors result in a difference of -44 

The factor pairs for 20 are
1,20
2,10
4,5
The factor pairs for 21 are
1,21
3,7

So now you use those pairs of numbers and try to find sums/difference of products that get you to -44

So let's try 2,10 and 1,21
Does 2*1 + 10*21 = -44 no
Does 2*21 + 1*10 = - 44 No
OK, let's try something esle
Try 2,10  3,7
Does 2*7 + 10*3 = -44 No, but it does equal 44. We are getting closer. All we need to do now is make the signs correct

{{{20x^2-44x+21}}}
{{{(2x - 3)(10x - 7)}}}

Here is a good URL for checking answers on this type of thing
http://72.3.253.76:8080/webMathematica3/quickmath/page.jsp?s1=algebra&s2=factor&s3=basic