You look for a common factor between the two terms, take it out, and use the distributive property.
15
What about it? Factorise it?
5a-20=
5a-20 = -15
2a
2
2a-5
5a + 20 = ? Your question is incomplete.
With the help of the quadratic equation formula
2a + 11a - 5a = 8a
2a+5
2(2x-11)(3x+5)