To work it out, you just need to know that there are 12 inches in a foot and 2.5 cm in an inch (roughly).
We want to convert 5 ft 8 in to cm.
5 ft = 5 x 12 = 60 in
Now add the 8 to 60, as we have quantities in the same unit
60 + 8 = 68 inches.
Now multiply by 2.5
There is an ease way to accomplish this:
2.5 = 25/10 = 5/2. So, to find the answer, you can multiply by 5 and divide by 2.
(60 + 8) x 5/2 = (300 + 40)/2 = 150 +20 = 170 cm
This is an approximation in fact there are 2.54 cm in an inch. If you want to get a precise answer, it's better to use an online calculator like this one:
Feet and inches to cm calculator