Abaseball diamond is a square with side 90 ft. a batter hits the ball and runs toward first base with a speed of 19 ft/s.

(a) at what rate is his distance from second base decreasing when he is halfway to first base? (round your answer to one decimal place.)
(b) at what rate is his distance from third base increasing at the same moment? (round your answer to one decimal place.)

So if you check the picture below, each side of the diamond has 90ft, so half-way from first to second is 45ft over the "x" line

a)

in this case, notice that "y" is static, is a constant, it doesn't change, whilst the  "r" distance is and the "x" as well, when the runner is going to 1st base



b)

well on this case, the distance "y" from home plate to 3rd base, isn't changing either, is a constant and is also 90ft as well