you need to add for number one you need to subtract for number two you need to add for number 3 you need to subtract for number 4
240 days is 4 times the half-life, which means that a sample of 1000 mg will decay to
after 240 days.
The answer is A,
if you plug in the points of (2,-5) into
y=x-7
-5=2-7
-5=-5
so the equation is true
X^2 = 1994
x= + - sqrt (1994)
Unfortunately, there is no integer that can suit x.