Answer:
x=3, y=1
Step-by-step explanation:
2x+y =7
3x-4y =5
Multiply the first equation by 4 so we can eliminate y
4(2x+y =7)
8x +4y =28
Add this to the second equation
8x +4y =28
3x-4y =5
----------------
11x = 33
Divide by 11
11x/11=33/11
x=3
Now we still need to find y
2x+y=7
2(3)+y =7
6+y=7
Subtract 6 from each side
6-6+y=7-6
y= 1
Answer:
h = 6
Step-by-step explanation:
Given the 2 equations
- 3x + 4y = - 30 → (1)
9x + 5y = 39 → (2)
We require the value of the x- coordinate at the point of intersection, thus require to eliminate the y- term from the equations
Multiply (1) by 5 and (2) by - 4
- 15x + 20y = - 150 → (3)
- 36x - 20y = - 156 → (4)
Add (3) and (4) term by term thus eliminating y
- 51x = - 306 ( divide both sides by - 51 )
x = h = 6
Choice A is the answer which is the point (1,-1)
=========================================
How I got this answer:
Plug each point into the inequality. If you get a true statement after simplifying, then that point is in the solution set and therefore a solution. Otherwise, it's not a solution.
-------------
checking choice A
plug in (x,y) = (1,-1)



This is true because -3 is equal to itself. So this is the answer.
-------------
checking choice B
plug in (x,y) = (2,4)



This is false because 0 is not to the left of -3, nor is 0 equal to -3. We can cross this off the list.
-------------
checking choice C
plug in (x,y) = (-2,3)



This is false because 7 is not to the left of -3, nor is 7 equal to -3. We can cross this off the list.
-------------
checking choice D
plug in (x,y) = (3,4)



This is false because -2 is not to the left of -3, nor is -2 equal to -3. We can cross this off the list.
To calculate the remaining caffeine, we use the radioactive decay formula which is expressed as An = Aoe^-kt where An is the amount left after t time, Ao is the initial amount and k is a constant we can calculate from the half-life information. We do as follows:
at half-life,
ln 1/2 = -k(6)
k = 0.12/hr
An = 80e^-0.12(14)
An = 15.87 mg