Question

Factorise 2a + 6 ?

I literally forgot how to factorise

Answer 1

You need to find a factor  of 2a and 6 - what number divides into both of these?  Its 2. 
so Dividing 2 into  2a + 6 gives you the other factor in the parentheses:-

Answer is 2(a + 3)

Answer 2

2a  + 6

2a + 2·3

2(a+3)