in one of the routine analyses, dr entropy found that the concentration of phosphate had increased from 0.0090 mg/l to 0.220 mg/l. this will require a lengthy investigation and detailed report into the causes. being the master of disorder, he considers an act of serious scientific misconduct - diluting the sample to reduce phosphate concentration to the maximum allowable level of 0.100 mg/l, and hoping that no-one notices.
if the volume of the original sample with concentration 0.220 mg/l is 10.0 ml, what should be the final volume of solution in order to dilute it to 0.100 mg/l?

linda: 3 ; laura: 15

step-by-step explanation:

note that linda + laura's age is 18, and that linda is 12 years younger than her sister.

let "linda" = x , "laura" = y:

x + y = 18

x = y - 12

first, plug in y - 12 for x in the first equation:

(y - 12) + y = 18

simplify.

2y - 12 = 18

isolate the variable (y). note the equal sign, what you do to one side, you do to the other. do the opposite of pemdas. first add, then divide.

2y - 12 (+12) = 18 (+12)

2y = 18 + 12

2y = 30

(2y)/2 = (30)/2

y = 30/2

y = 15

next, plug in 15 for y in the second equation (the other equation would work too).

x = y - 12

x = (15) - 12

x = 3

linda's age is 3, laura's age is 15.

~

the answer is c. nacl