Answer:
2.5mph
Step-by-step explanation:
S = Distance divided by Time (S = D/T)
Therefore.
S = 15/6
=2.5 mph
Colin walked an average speed of 2.5mph
Answer: k=3
Step-by-step explanation:
To solve for k, you want to isolate k.
[add both sides by 8]
[multiply both sides by 5/2]
[subtract both sides by 35]
[divide both sides by 5]

Now, we know that k=3.
A suitable calculator* can do this easily.
61°38'45" = (61 +(38 +45/60)/60)° ≈ 61.65°
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I like the RealCalc app for Android, but many graphing calculators also will do this conversion. Of course, you can simply evaluate the expression as above.
The density of the gold is 772.8 kilograms\cubic meters