Ok im grade 10 now but why is my module so easy

HAHAHAHHAA LOL​

Given this information, which expression must represent the value of b?

What is the value with a place of tenths in 907.456 1) 0 2) 6 3) 4 4) 5

Parabolas y=−2x^2 and y=2x^2+k intersect at points a and b that are in the third and the fourth quadrants respectively. find k if length of the segment ab is 5.