Question

what is the value of y in the equation 6.4x + 2.8y = 44.4, when x = 3?
○ y = 5
○ y = 6
○ y = 8
○ y = 9

Explanation:

Step1: Substitute x = 3 into the equation

Substitute \( x = 3 \) into \( 6.4x + 2.8y = 44.4 \), we get \( 6.4\times3 + 2.8y = 44.4 \).
Calculate \( 6.4\times3 = 19.2 \), so the equation becomes \( 19.2 + 2.8y = 44.4 \).

Step2: Solve for y

Subtract 19.2 from both sides: \( 2.8y = 44.4 - 19.2 \).
Calculate \( 44.4 - 19.2 = 25.2 \), so \( 2.8y = 25.2 \).
Divide both sides by 2.8: \( y=\frac{25.2}{2.8}=9 \)? Wait, no, wait, 25.2 divided by 2.8: 2.89=25.2? Wait, 2.89=25.2, but let's check again. Wait, 6.43 is 19.2, 44.4-19.2 is 25.2, 25.2/2.8: 2.89=25.2? Wait, 2.89=25.2, yes. But wait, the options have y=9? Wait, the options are y=5, y=6, y=8, y=9. Wait, maybe I miscalculated? Wait, 6.43: 63=18, 0.43=1.2, so 18+1.2=19.2. Then 44.4-19.2=25.2. 25.2 divided by 2.8: 2.8*9=25.2, so y=9. Wait, but let's check again. Wait, maybe the equation is 6.4x + 2.8y = 44.4. Wait, maybe I made a mistake in substitution? Wait, no, the steps are correct. So the answer should be y=9. Wait, but the options include y=9. So the correct option is y=9.
Wait, but let's check again. Let's plug y=9 back into the equation: 6.43 + 2.89 = 19.2 + 25.2 = 44.4, which matches the right-hand side. So that's correct.

Answer:

y = 9