Question

Related Rates
A spotlight on the ground shines on a wall 12 m away. If a man 2 m tall walks from the spotlight toward the building at a speed of 2.1 m/s, how fast is the length of his shadow on the building decreasing when he is 4 m from the building?
I cant figure out what db/dm is. b(building) m(man). I can solve it once I get that.

Answer 1

you know that
\[\frac{y}{12}=\frac{2}{x}\] and you also know
\[x'=2.1\]so you can solve for
\[y'\] i think

Answer 2

I need to relate distance from the building to y, not distance from the light. Its a start though.

Answer 3

actually you need
\[y'\] the rate of the shadow against the wal.