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: 2.8 times 9 is 25.2? Wait, 2.89=25.2? Wait, 2.89: 29=18, 0.89=7.2, 18+7.2=25.2. But wait, let's check again. Wait, 6.43 is 19.2, 44.4 - 19.2 is 25.2. Then 25.2 / 2.8. Let's do 25.2 ÷ 2.8. Multiply numerator and denominator by 10: 252 ÷ 28. 289=252, so y=9? But wait, let's check the options. Wait, maybe I made a mistake. Wait, 6.43: 63=18, 0.43=1.2, so 18+1.2=19.2. Then 44.4 - 19.2 = 25.2. Then 25.2 / 2.8. Let's compute 2.89=25.2, so y=9? But the options have y=9 as an option. Wait, but let's check again. Wait, maybe I miscalculated. Wait, 6.4x + 2.8y = 44.4, x=3. So 6.43=19.2. 44.4-19.2=25.2. 25.2/2.8=9. So y=9. Wait, but let's check the options. The options are y=5, y=6, y=8, y=9. So the correct answer is y=9? Wait, but wait, maybe I made a mistake. Wait, 2.89=25.2, 19.2+25.2=44.4, which matches the equation. So yes, y=9.

Wait, but wait, let me check again. 6.43=19.2. 44.4-19.2=25.2. 25.2 divided by 2.8: 2.89=25.2, so y=9. So the answer is y=9.

Answer:

\( y = 9 \) (the option with \( y = 9 \))