X = rivet
You have 5 rivets and 4 intervals (spaces between the Xs).
Rite masters is rite, consider it like this, you have 28 rivets, and each one should have 35.2 millimeters in front of it before the next rivet, so logically, you would think 28*35.2, HOWEVER, you don't include the distance after the last one because there isnt another rivit after it.
So you have 27 instead, then u have 27*35.2= 950.4 , this is the right answer.
Hope this helped.