1) calculate  of 7kg. 

"Of" means "times"

So  of 7kg  means

 times 7kg  or

 × 7kg

We write 7kg as kg so we have

×kg

We multiply the two numerators 4×7 and get 28 for the final numerator
We multiply the two denominators 5×1 and get 5 for the final denominator

kg

but that is an improper fraction so we do this division:

   5 
5)28
  25
   3

The whole part is 5 and the fractional part is gotten by
putting the remainder 3 over the divisor 5 and we get 

kg
2) 3/4 of 5km.       <--- answer = km
3) 4/6 of 2 days.    <--- answer = days
4) 6/7 of 63litres.  <--- answer = litres
5) 5/8 of R960       <--- (Was the R a typo?)  5/8 of 960 gives 600 
6) 5/6 of 3hrs       <--- answer =  hrs 
7) 9/12 of 132       <--- answer = 99

Edwin