It is exponent laws. my teacher said x is 3 but i don't get why

Ametalworker has a metal alloy that is 30? % copper and another alloy that is 55? % copper. how many kilograms of each alloy should the metalworker combine to create 90 kg of a 50? % copper? alloy?

Which solid has two triangular bases and three lateral faces, each in the shape of a rectangle? triangular prism triangular pyramid rectangular prism rectangular pyramid

What is the value of x? enter your answer in the box.