The answer is 4x + 5y.
Here, what needs to be done is to combine like terms.
- 5x + 4y + 3x - 7y - 4x + 8y
- 5x + 3x - 4x + 4y + 8y - 7y
- 4x + 5y
First, you must change all of this into improper fractions, like shown below.

Now you must change the sign.

Then we must reciprocalize 2/3.

Now we multiply, to get 2 4/10.
<span>When order does not matter you use what is called n choose k formula
n!/(k!(n-k)!) where n is the number of things to choose from and k is the number of choices made, in this case:
20!/(4!(20-4)!)=4845</span>
Our first expression is equal to zero:

So we simply find the expression that is equal to zero.
The final answer is a.
18 and 3/7
Because i can write by phone. So just write 18 in the left side of 3/7