Your partition points are $x_0=7,~x_1=7.25,~x-2=7.5,~x_3=7.75,~x_4=8$ where $\delta x=0.25$
$LHS=\displaystyle\left( {\sum\limits_{k = 0}^3 {f({x_k})} } \right)\left( {0.25} \right)$
$RHS=\displaystyle\left( {\sum\limits_{k = 1}^4 {f({x_k})} } \right)\left( {0.25} \right)$
You do the hard work.