$$3)$

An overhead door is guided by wheels at A and $B$ that roll in horizontal and vertical tracks. Knowing that when $=40$ the velocity of wheel $B$ is $1\mathrm{.}5f\frac{t}{s}$ upward, determine $($a$)$ the angular velocity of the door, $($b$)$ the velocity of end $D$ of the door.

using: $-$ instantaneous centers