To use the elimination method, you can add the two equations in a system of equations to eliminate one of the variables. Add the two equations.
{−9x+y=1010x−y=−9

What is the resulting equation?
Answers :

A 0+2y=10 plus 2 y is equal to 1

B x+0=1x plus 0 is equal to 1

C x+0=19x plus 0 is equal to 19

D 19x+2y=19

answer is  

c.

36

step-by-step explanation:

the answer would be c

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

source:  

y= -2x+4, have a great day