Answer
$a=1.54 \mathrm{~m}$
Work Step by Step
$
\begin{array}{rlrl}
+\uparrow F_R=0=\Sigma F_y ; & 0 & \\=\frac{1}{2}(2.5)(9)-\frac{1}{2}(4)(b) \quad b=5.625 \mathrm{~m} \\
\varsigma+M_{R A}=\Sigma M_A ; & -8 & \\=-\frac{1}{2}(2.5)(9)(6)+\frac{1}{2}(4)(5.625)\left(a+\frac{2}{3}(5.625)\right) \\
a =1.54 \mathrm{~m}
\end{array}
$
