50 is what percent of 40?

Which addition property is being illustrated below? (type commutative or associative) (6 + 7) + 1 = 6 + (7 + 1)

What is the length of the unknown leg in the right triangle ?

F(x) = 1/x g(x)=x-4 can you evaluate (g*f)(0) ? why or why not?