Answer : 38 kmph
egin{aligned} ext{D1=70 km}\ ext{T1=1 hr}\ ext{D2=120 km}\ ext{S2=30 km/hr}\ ext{Average speed=}frac{2xy}{left(x+y
ight)}\ ext{T2 = }frac{120}{30}=4 hr\ ext{S1=}frac{D1}{T1}=frac{70}{1}= 70 km/hr\ =frac{2*70*30}{left(70+30
ight)}\ =frac{2*2100}{100}=2*21=42 km/hr\ end{aligned}