Question 835124
d/2=9d/18 because 1/2*d=9/18*d
r*t=d
t=d/r
t=d/2
t=d/18
total time is 10 so add the two time parts of the round trip to get the total time
so from the beginning

d/2+d/18=10
find common denominator which is 18
1/2*d=9/18*d
9/18*d+d/18=10

10/18*d=10
divide by 10
d/18=1
d=18