To find M from that series of data, you'd just have to fill out the simple equation of (5x)+(7x+8)+(7x+3)=163. Group like terms to get 19x+11=163. Subtract 11 from 163 to get 19x=152. 152/19 is 8. X is 8. Plug that in each side to get 40m, 64m and 59m, in the same order of (5x)+(7x+8)+(7x+3)
TL;DR of it all:
(5x)+(7x+8)+(7x+3)
40m, 64m, 59m. Don't forget the unit of measurement.