The first one, the opposite of any negative number is the same number but positive...and vise versa.
Because it is a question asking for ppl playing either soccer OR basketball, we add the two fractions together. Thus, Part A becomes 3/10 + 4/10, which is 7/10 (since the denominators are the same, you only add the numerators).
Should be equal to. sorry if its incorrect, but that's what i would go with.
Given the equation
.
When x is maximum, we have
. Hence 
The maximum temperature is 
When x is minimum, we have
. Hence 
The minimum temperature is 