me assume yu want a rite triangel with hite=20 & diagonal=80
80^2 -20^2=quuare av base leng
b^2=6400=400=6000
base=sqrt(6000)
base=77.45966692 ft
or bout 77.46ft
Or yu kan just yuze the invers sine(20/80)=sine-1(1/4)
invers sine(0.25)=14.477512185924283 deg
or bout 14.48 deg