a level is set up midway between two stakes as shown in the figure below. The two stakes are about $200$ feet apart. The rod reading on stake A is $8\mathrm{.}72$ feet and the rod reading on stake B is $5\mathrm{.}61$ feet. The level is then moved to point B and set up so that the eyepiece end of the telescope is just touching the rod as it is held plumb on the stake. A reading of $5\mathrm{.}42$ feet is taken from the rod at B by sighting backward through the telescope.

$1)$What is the correct difference in elevation between the tops of stakes A and B$?$