Acrystallographer measures the horizontal spacing between molecules in a crystal. the spacing is 14.8 nm . what is the total width of a crystal in millimeters 105 molecules across? write your answer as a decimal.

1539.2nm

The space between molecule is going as X-1 function. That mean 1 molecule doesn't have space, 2 molecules have 1 space, 3 molecules have 2 space. Then 105 molecules will be will have 104 space.
Each space is 14.8nm, the total  distance would be: 104 space x 14.8 nm/space= 1539.2nm