Hi
Let c represent the speed of the current
Question states*** time is the same Note: t = D/r
1.5/(6+c) = 1/(6-c) |cross Multiplying
6 + c = 1.5(6-c)
2.5c = 3
c = 1.2kmph
CHECKING our Answer***
1.5/7.2 = 1/4.8 = .2083hr
As to Your further question:
A.= (3/8x)(12x/5)= 36/40 = 9/10
B. 4/15y/12/5y = (4/15y)(5y/12) = 1/9