If x varies directly with y, and x=9 when y =6, find x when y = 15 explain

Direct variation problems use the equation y = kx

Replace y and X with the two known numbers to solve for k:

6=k9

Solve for K by dividing both sides by 9:

k = 6/9, reduces to 2/3

Now replace y and k into the formula to solve for x:

15 = 2/3x

Solve for X by dividing both sides by 2/3:

X = 15 / 2/3

X = 45/2 as an improper fraction, 22 1/2 as a proper fraction or 22.5 as a decimal.

Not sure which format the answer needs to be in, so I gave all three.

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is: