find the sum of the following expressions show your solution

1.
[tex]2a \: + \: 3a \: + 7a \: + \: a = [/tex]
2.
[tex]( - 2y \: - 4) \: (5y \: + \: 6) = [/tex]
3.
[tex]6a {}^{3} - 5a {}^{2} b - 4b {}^{2} \\ - 5a {}^{3} + 6a {}^{2} b + 8b {}^{2} [/tex]
4.
[tex](5b + 8m) + ( - 3b - \: 12m)[/tex]
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