Equivalent expression for (x+6)-5+9

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?

Apair of ordinary dice is rolled. what is the probability that each die will show a number higher than 4. 1. (1/36) 2. (1/12) 3. (1/6) 4. (1/4) 5. (1/3)

What is the number 321,000,000 in scientific notation? also what is the number? ?