Answer:
The amount of drug left in his body at 7:00 pm is 315.7 mg.
Explanation:
First, we need to find the amount of drug in the body at 90 min by using the exponential decay equation:

Where:
λ: is the decay constant = 
: is the half-life of the drug = 3.5 h
N(t): is the quantity of the drug at time t
N₀: is the initial quantity
After 90 min and before he takes the other 200 mg pill, we have:

Now, at 7:00 pm we have:

Therefore, the amount of drug left in his body at 7:00 pm is 315.7 mg (from an initial amount of 400 mg).
I hope it helps you!
Explanation:
The electrical force between two objects is given by the formula as follows :

k is electrostatic constant
q₁ and q₂ are electric charges
d is distance between charges
So, the two force between two charged objects depends on the product of charges and distance between charges.
Answer:
The one left in the hot sunlight.
Explanation:
The solubility of gases decreases when temperature increases. The gas in the soda pop (CO2) left in the sun will not stay dissolved as much as the on left in the refrigerator.
Answer:
The answer to your question is A.
Pure substances can not be broken down into others, so they cannot be molecules
Explanation: