Systems of linear equations i really dont know how to do this : ')

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

Deshawn uses 3/4 of a box of rice to cook dinner the portion he uses weighs 12 ounces right and solve an equation to find the weight of the full box of rice

Given that sin∅ = 1/4, 0 < ∅ < π/2, what is the exact value of cos∅? a. (√4)/4 b. (√15)/4 c. (4π)/2 d. (4√2)/4