1) Examining the expressions, let's factorize them taking the LCM out of the parentheses
5a +10 The LCM 5,10 is 5
5(a +2)
16k +12 The LCM 16, 12 is 4
4(4k +3)
2) So the answers are 5(a +2) and 4(4k +3) notice that if we distribute those factors you'll get the initial form.