5{-3.4k-7} + {3k+21}

First step is to do distributive property.

so you multiply 5 by - 3.4k and - 7

your equation now is - 17k-35 + (3k+21)

Then you add like terms

add - 17k+3k to give you - 14k-35+21

then you add like terms again

add - 35+21 to give you - 14

so now your equation is - 14k-14

So that is your answer simplified