If Josiah’s speed, in miles per minute, is constant, what is the constant of proportionality?

Ineed me i stuck and i don’t want to get it wrong

The fence around a quadrilateral-shaped pasture is 3a^2+15a+9 long. three sides of the fence have the following lengths: 5a, 10a-2, a^2-7. what is the length of the fourth side of the fence?

A11 gram sample of a substance that’s used to treat thyroid disorders has a k-value of 0.1247