Answer:

Step-by-step explanation:
Since we see that 3/7 is multiplied by itself three times, we can use exponents as a shorter way to write this. The expontent tells us how many times the base number, 3/7, is multiplied by itself.
= 
We then multiply by -1 to (3/7)^3 to get the exact answer.

2(2x) + 1x = 40 or 4x + 1x = 40 is the result of combining by substitution
<em><u>Solution:</u></em>
Given that we have to combine 2y + 1x = 40 and y = 2x using substitution method
The substitution method for solving systems of equations involves expressing one variable in terms of another, thus removing one variable from an equation.
<em><u>Given equations are:</u></em>
2y + 1x = 40 -------- eqn 1
y = 2x ----------- eqn 2
We can substitute eqn 2 in eqn 1
Which means, substitute y = 2x in place of y in eqn 1
2(2x) + 1x = 40
4x + 1x = 40
5x = 40
x = 8
From eqn 2,
y = 2(8)
y = 16
Thus by combining using substitution method we found the solution
Answer: D
Step-by-step explanation: It fills the requirements