Factor by grouping 5x^2+40x-x-8

"Factor by grouping" generally means you divide the 4 terms into groups of 2 terms.

... (5x^2 + 40x) - (x + 8)

Now, you factor each group.

... 5x (x + 8) - 1 (x + 8)

Now, you factor out the common factor, x+8.

... (5x - 1) (x + 8)