You have to use the distance formula for lengths of XZ, ZY, and YX. Filling in the formula for the distance that they provided,
and
which is
which, in decimal form is 12.5299. Now onto the next length, ZY:
and
which is
which, in decimal form is 6.70820. Now onto the last segment, YX:
and
and of course the square root of 14 squared is 14. So our sides lengths are, for the perimeter, 12.5299+6.70820+14=33.2 units.