First, we {{CMD_218}}introduce a variable{{CMD_219}} {{MATH_220}}, the distance the plane has traveled after it flew right above you. So, the given rate is {{MATH_221}} mph and the unknown (related) rate is {{MATH_222}}, at the instant when {{MATH_223}} miles. This rate should be measured in rad/s. Therefore, we have to convert the units of the given rate, mph, into mi/s: {{MATH_224}}mph{{MATH_225}} mi/s. {{CMD_226}} Next, we {{CMD_227}}draw a picture{{CMD_228}}. {{CMD_229}} {{ENV_230}} {{CMD_231}} Now we {{CMD_232}}find an equation{{CMD_233}} relating variables {{MATH_234}} and {{MATH_235}}. From the picture we can see that {{MATH_236}} Since {{MATH_237}} and {{MATH_238}} are both functions of time, we now {{CMD_239}}differentiate{{CMD_240}} both sides of the equation. We write {{MATH_241}} The above equation holds over some interval of time. In particular, it is true when {{MATH_242}}. Therefore, when {{MATH_243}}, {{MATH_244}} This implies that we have to compute the unknown value, {{MATH_245}}, when {{MATH_246}}. To this end, we draw and label the picture at the time when {{MATH_247}} mi. {{CMD_248}} {{ENV_249}} {{CMD_250}}