To find the value of \( x \) in the equation \( 4x + 8y = 40 \) when \( y = 0.8 \), we can follow these steps:
1. Substitute \( y \) with 0.8 in the equation:
[tex]\[
4x + 8(0.8) = 40
\][/tex]
2. Multiply 8 by 0.8:
[tex]\[
8 \times 0.8 = 6.4
\][/tex]
3. Substitute the result back into the equation:
[tex]\[
4x + 6.4 = 40
\][/tex]
4. Isolate the term involving \( x \) by subtracting 6.4 from both sides:
[tex]\[
4x = 40 - 6.4
\][/tex]
5. Perform the subtraction on the right side:
[tex]\[
40 - 6.4 = 33.6
\][/tex]
6. Now, we have:
[tex]\[
4x = 33.6
\][/tex]
7. Solve for \( x \) by dividing both sides by 4:
[tex]\[
x = \frac{33.6}{4}
\][/tex]
8. Perform the division:
[tex]\[
x = 8.4
\][/tex]
Therefore, the value of [tex]\( x \)[/tex] is [tex]\( 8.4 \)[/tex]. So, the correct answer is [tex]\( 8.4 \)[/tex].
