For this case we can define the following variable:
x: unknown number
We write the equation that models the problem:

From here, we clear the value of x.
We have then:

Answer:
Completing the sentence we have:
0.04 is 1/10 of 0.40
1/40 = .025, just multiply this by 21 and you have your answer
.525
Step-by-step explanation:
3x - 9 +2x + 9 = 2x - 2
5x = 2x - 2
5x - 2x = - 2
3x = - 2
x= - 2/ 3
It would be y=4x-2 because:
8x-3y=6-4x
-8x -8x
-3y=6-12x
/-3 /-3 /-3
y=-2+4x
y=4x-2