8 meters is equivalent to 8000 millimeters, 1 meter = 1000 milimeters
Hope this helps
Answer to Q2:
Can't really do a tree diagram here but the combinations are:
NN
NR
NW
NG
RN
RR
RW
RG
WN
WR
WW
WG
GN
GR
GW
GG
That's 16 combinations, 4 of which are matching both pants and shirt. 4/16 = 1/4. So there's a 25% chance of a matching outfit.