$4.$ In a two$-$peg test, the following observations were taken. Point P is equidistant from A and B and Q is $12$m from A and $72$m from B$.$ What is the true difference in elevation between A and B$?$ Instrument at Instrument at Q S$2$: D$.-$D$\mathrm{.}250.$SUg P b$-702$ Rod reading on $1\mathrm{.}1030\mathrm{.}568$

$>$ Rod reading on B

$0\mathrm{.}991$

$0\mathrm{.}289$