A support wire stretches from the top of a pole that is 30 feet tall to an anchor in the ground 40 feet from the base of the pole. How long is the wire?

Basically you have a right triangle with one leg measuring 30 feet and the other measuring 40 feet. You are looking for the hypotenuse of this triange.

You can use Pythagorean theorem to solve:

c²=a²+b²

c²=30²+40²

c²=900+1600

c²=2500

c=√2500

c=50 feet

OR, if you recognize the Pythagorean triple pattern of 3, 4, 5, you would know that the hypotenuse would be 50 feet

L^2=y^2+x^2

L^2=30^2+40^2

L^2=900+1600

L^2=2500

L=50ft