Algebra.

Easy- 

2(4+5)= 2x4= 8         2x5=10 

so it would be; 8+10

Medium-  

3x(5+11)= 3xX5=15x 3xX11=33x 

so it would be; 15x+33x

Hard- 

12x(2-3)= 12xX2=24    12xX3=36x

so it would be; 24x-36x

Factorising is putting things back into brackets whereas expanding is getting rid of brackets. 

Easy-

3x+6 (find the common multiplier)

3x= 3X1Xx 

6= 3X2 (the common multipler is 3.)

So the 3 goes outside the brackets and the rest goes inside. 

3(x+2) (the numbers inside are the left over ones and the ones which aren't common)