Depth d (in feet) of a river can be modeled by the equation d=−0.25t2+1.7t+3.5, where 0≤t≤7 and t is the time (in hours) after a heavy rain begins. When is the river 6 feet deep?

The river is 6 feet at two times, 2.15 hours after the rain and 4.65 hours after the rain.

Step-by-step explanation:

We are given the following in the question:

where, d is the depth of river in feet and t is time in hours after a heavy rain.

We have to find the number of hours for which the depth of river is 6 feet.

Putting d = 6 in the equation, we get,

Thus, the river is 6 feet at two times, 2.115 hours after the rain and 4.65 hours after the rain.

The attached image shows the graph.