The distance from home plate to the fence in dead center in wrigley field is 400 feet. how far is it from the fence in dead center to third base? how far is it from the fence in dead center to second base?

The sides of  a baseball field are 90 feet.
That means that a line from 3rd base to the pitcher's mound is (1/2) * sqrt (2*90^2) = 63.64 feet
The distance between the pitcher's mound and the plate is also the same
distance between pitcher's mound and homerun wall = 400 - 63.64 = 336.36 feet
Distance to 3rd base = sqrt(63.64^2 + 336.36^2)  = 342.33 feet

hope this helps