−10+6(−2t+4)

Do multiplication before you do either additions and subtractions, so simplify 6(-2t + 4) by using the distributive property.

-10 + 6(-2t + 4)

=  -10 +6(-2t) + (6)(4)

=  -10 - 12t + 24

Now, simplify like terms:

=  14 - 12t