Question

Factorise 3a squared + 7a

Answer 1

GCF: 1 (3 cant go into 7 and the other way around in whole number terms.)
So, 1 is the factor you are distributing.
1 goes into 3 three times. 
1 goes into 7 seven times.
Don't forget your variable!

So the answer is: a(3a+ 7).

Answer 2

To factorise this we have to first find the biggest common factor. 3 and 7 are both are prime numbers so we can't factorise it by a number. but both numbers have an 'a' so we have to factorise it by a. hence the answer is,
a(3a+7).
hope it helps.