multiply the 20 and the 80 together, getting 1600. find two factors of that which equals 116. in this case, it is 100 and 16. so now youd get 20x^2 +100x +16x+80: factor out by grouping, now. 5x(4x+20) +4(4x+20): your factors are (5x+4) and (4x+20), which gives you x=-4/5, -5 (but thats only if you need it).