The temperature was very cold, then it dropped 10 degrees, and then it increased by 40 degrees. The temperature is now 16 degrees. What was the starting temperature

-14 degrees

You just have to work your way backwards. Start with 16 degrees then subtract 40 (instead of adding) and then add 10 (instead of subtracting). If you want to double check if you got it right, just start with your answer and do what the problem says ... - 14-10+40. You should get what the current temperature is (16 degrees)