Required information

Problem $15\mathrm{.}039-$ Overhead door guided by wheels in horizontal and vertical tracks

An overhead door is guided by wheels at A and $B$ that roll in horizontal and vertical tracks. Know that when $=30$ the velocity of wheel $B$ is $3f\frac{t}{s}$ downward.

Problem $15\mathrm{.}039.$b $-$ Velocity of the end of the overhead door

Determine the velocity of end $D$ of the door. $($Round the final answer to three decimal places. Include a minus sign if necessary.$)$

The velocity of end $D$ of the door is $($ i $+$ j$)$ ft$/$s$.$