Plz help, I'll give brainliest

Find the value of x​

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

Determine the number of girls in a math class with 87 boys if there are 25 girls for every 75 boys

Aball is thrown from a height of 139 feet with an initial downward velocity of 15 ft/s. the ball's height h (in feet) after t seconds is given by the following. h=139-15t-16t^2 how long after the ball is thrown does it hit the ground? round your answer(s) to the nearest hundredth. (if there is more than one answer, use the "or" button.) t =