linear equation problem solving

Need help on these questions..

question 1- show that 2/c = 1/a+1/b

attempt:

2ab=bc + ac...

question 2 - Xiu travels from town A to B at u km/h and then returns at v km/h. Town A is d km from town B

a) if i t takes T hours to travel from A to B, find the time taken:

i) the entire trip in terms of T, u and v

attempt:

time = distance/ speed

u + v =speed back and forth

distance is d km

so d/u+v ??

question 3- A man walks 70 km. He walks x km at 8 km/h and y km at 10km/h

a) fins his average speed in terms of x and y.

attempt:

average speed is = distance/ time

70/8x+10y ??

thanks!