7th grade math help me please

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?

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.

15m is what percent of 60m; 3m; 30m; 1.5 km? the last one is km not m