Whats the equation that represents y

To decrease an amount by 16% what single multiplier would you use

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?

If you were constructing a triangular frame, and you had wood in the length of 4inches, 4 inches, and 7 inches, would it make a triangle? would you be able to create a frame from these pieces of wood? yes or no. explain your mathematical thinking