The answer is D, i.e. the system was solved via elimination
If you multiply the first equation by 5, the system becomes
If you sum the two equations, you get
And so if you substitute the second equation of system A with this new equation, you'll get system B.
The answer is 7/5 th. You can add fractions without first having a common denominator so you would change the 8's by multiplying it by 5 to get 40 and you would multiply the 5 by 8 to get 40 as well. And the rule whatever you do to the bottom you have to do to the top so whatever you multiplied 8 by do the same for the numerator and whatever you multiplied 5 by you do the same for the numerator. So your new equation would be (75/40+16/40)+(-35/40). you would then add the numerator's across to get 56 and the denominator would stay the same so the answer is 56/40. But you have to now simplify 56/40 down to 14/10 and then once more to 7/5 which is the final answer.
75% of the gallon of milk is left
16/16-4/16=12/16
12/16=3/4=0.75
