What is the fastest and easiest way to find hcf ( highest common factor)
and lcm ( lowest common multiple)

If the small number is a factor of the larger then the GCF is the smaller number. In this case its easy and fast.
If the numbers are not in that form then one way is to find the prime factors of each number and find the GCF by comparing them 

For example  Find the GCF of 44 and 84:-

44 = 2 * 2 * 11
84 = 2 *  2 * 3 * 7

 Pick out the common numbers . Here there are 2 pairs of the number 2 So the GCF = 2*2 = 4

LCM :-  One way is to multiply  the 2 numbers together and see if there is a lower number 

For example:-   LCM of    12 and 8 
12 * 8 = 96  - divide by 2 gives 48 which is divisible by 6 and 8. Now try  dividing by 2 again = 24   This also could be the LCM. Divide by 2 gives 12 but 8 will not divide into 12 so the LCM is 24.

THis is OK for relatively low numbers but for bigger ones you can  use the method of prime factors.

for example:-

LCM of 88 and  16:;-

88 = 2*2*2*11
48 = 2*2*2*2* 3
Foe each duplicate 2  just use  one 2 and also include the odd ones 2 , 3 and 11:_

LCM = 2*2*2*2*3*11 = 528

127 millimeters is the answer