Solution to Problem 679 | Midspan Deflection

$EI \, t_{A/B} = (Area_{AB}) \, \bar{X}_A$

$EI \, t_{A/B} = \frac{1}{2}(6)(720)(4) - \frac{1}{4}(4)(160)(\frac{26}{5})$

$EI \, t_{A/B} = 7808 \, \text{ lb}\cdot\text{ft}^3$
 

$EI \, \delta = \frac{1}{2}(EI \, t_{A/B})$

$EI \, \delta = \frac{1}{2}(7808)$

$EI \, \delta = 3904 \, \text{ lb}\cdot\text{ft}^3$           answer