Can 7,9,16 be a right traingle​

Apatient is given 50 mg dose of medicine the medicines effectiveness decreases every hour at a constant rate of 40% what is the exponential decay function that models this scenario how much medicine will be left in the patients system after 2 hours

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much

Wrote and expression for the difference of p and 4