1.7 hrs
Step-by-step explanation:
We can use cosine law to find the distance d:
where. a = 3 mi
b = 4 mi
gamma = 71.7°
d^2 = (3mi)^2 + (4 mi)^2 - 2(3 mi)(4 mi)cos(71.7)
= 9 mi^2 + 16 mi^2 -24cos(71.7)
= 17.464 mi^2
or
d = 4.2 mi
To find the time it takes for him to go from the cave to the waterfall, divide this distance d by his walking rate of 2.5 mi/hr:
t = d/v = 4.2 mi/2.5 mph
= 1.7 hrs