What is the property of this equation? if 2x=8 then x=4

The perimeter of a triangle is 69 cm. the first is 5 cm shorter than the second side. the third side is twice as long the first side. find the length of each side

Find the domain and range of the following function f(x) = 51x - 21+ 4

Aboard 60 in. long is cut two parts so that the longer piece is 5 times the shorter. what are the length of the two pieces?