18 + (-8) + 11
Adding a negative number is the same as subtracting a positive number. So "18-8" is the same thing as "18+ -8".
18 - 8 + 11
10 + 11
21
Answer:

Step-by-step explanation:
I think the answer is: 6 = -21
Answer: 6 weeks
Step-by-step explanation: $54 x 6 = $324
Let's give some distances
100 up 100 flat 100 down meters
then return 100 up 100 flat 100 down
time required (distance/rate = time ) 200/100 + 200/120 + 200 / 150 = 5 hr
distance 600
distance / time = average speed = 600/5 = 120 m/s