Two points l and n are 160 m apart. m lies on the straight line joining l and n. an object travels from l to m at an average speed of the object for its entire journey from l to n 10 m/s in 6 seconds and then from m to n at an average speed of 25 m/s. find the average

For the first question:

-8.3 - (-5.4)

This is -8.3 minus negative 5.4

The two negatives equal a positive, so he should have replaced them with a + sign:

-8.3 + 5.4

Instead, he subtracted 5.4 from -8.3 and got A.

For the second question, find a common denominator so that you can add the fractions together. 8 and 3 both fit into 24, so use that as your denominator. To get from the denominator 8 to the denominator 24, you multiply by 3. So multiply the numerator (7) by 3 as well. So that fraction becomes 21/24

To get from denominator 3 to 24, you multiply by 8. So do the same thing to the top. You then have 16/24. The change in the amount of water is 16/24 cups. That can be simplified to 2/3