$R_A = 4(1) = 4 \, \text{kN}$
$M_A = 4(1)(2.5) = 10 \, \text{kN}\cdot\text{m}$
$t_{B/A} = \dfrac{1}{EI}(Area_{AB}) \, \bar{X}_B$
$t_{B/A} = \dfrac{1}{69\,000\left[ \dfrac{50(150^3)}{12} \right]} \, [ \, \frac{1}{2}(3)(12)(1) - 3(10)(1.5) - \frac{1}{3}(1)(2)(0.25) \, ]\,(1000^4)$
$t_{B/A} = -28 \, \text{mm}$
∴ δmax = 28 mm answer