You can FOIL (First, Outside, Inside, Last)
(3z+1)(4z+2)
First
(3z+1)(4z+2)
3z * 4z
Outside
(3z+1)(4z+2)
3z * 2
6z
Inside
(3z+1)(4z+2)
4z * 1
4z
Last
(3z+1)(4z+2)
2*1
2
Combine all the products of FOIL together
+ 6z + 4z + 2
Combine like terms
+ 10z + 2
Hope this helped!
~Just a girl in love with Shawn Mendes