To find the value of [tex]\( x \)[/tex] in the equation [tex]\( 4x + 8y = 40 \)[/tex] when [tex]\( y = 0.8 \)[/tex], follow these steps:
1. Substitute the given value of [tex]\( y \)[/tex] into the equation:
Given equation:
[tex]\[
4x + 8y = 40
\][/tex]
Substitute [tex]\( y = 0.8 \)[/tex]:
[tex]\[
4x + 8(0.8) = 40
\][/tex]
2. Calculate the value inside the parenthesis:
Compute [tex]\( 8 \times 0.8 \)[/tex]:
[tex]\[
8 \times 0.8 = 6.4
\][/tex]
3. Substitute back into the equation:
Now the equation looks like:
[tex]\[
4x + 6.4 = 40
\][/tex]
4. Isolate the term with [tex]\( x \)[/tex]:
Subtract 6.4 from both sides to isolate [tex]\( 4x \)[/tex]:
[tex]\[
4x + 6.4 - 6.4 = 40 - 6.4
\][/tex]
[tex]\[
4x = 33.6
\][/tex]
5. Solve for [tex]\( x \)[/tex]:
Divide both sides by 4:
[tex]\[
x = \frac{33.6}{4}
\][/tex]
Finally, compute:
[tex]\[
x = 8.4
\][/tex]
Therefore, the value of [tex]\( x \)[/tex] is [tex]\( 8.4 \)[/tex].
The correct choice is:
[tex]\[ \boxed{8.4} \][/tex]
