Question 907046
r*t=d
t=d/r
20/50+20/60+20/x=1
2/5+1/3+20/x=1
6/15+5/15+20/x=1
11/15+20/x=1
20/x=4/15
300=4x
x=75 mph
check
20/50+20/60+20/75=1
6/15+5/15+4/15=15/15
6+5+4=15
ok