What does this equal
-2×(3+18÷3)-6

Lets do the operations step by step and lets give it precedence to the division before the addition and the multiplication before the subtraction:
-2×(3+18÷3)-6
= -2 x (3 + 6) - 6
= -2 x (9) - 6
= -2 x 9 - 6
= -18 - 6
= -24

Think of it as five or above give it a shove. change the 5 or above to the right to a zero and add one to the number on the left.