### Home > CALC > Chapter 11 > Lesson 11.1.2 > Problem 11-26

11-26.

A 4-foot tall child walks away from a 12-foot street light at a rate of 2 feet per second. At what

rate is the length of her shadow increasing when she is 6 feet away from the light? Homework Help ✎ 1 ft/sec

2 ft/sec

3 ft/sec

4 ft/sec

6 ft/sec

Sketch the situation. Your sketch should have similar right triangles.

If the child's distance from the light is *d* and their shadow length is *s*, then:

The equation can be rewritten as 2*s* = *d*.

Now differentiate.

Now use the information given in the problem to solve for *ds*/*dt*.