Answer :

Certainly! Let's solve the problem step-by-step.

Given the equation [tex]\( 4x + 8y = 40 \)[/tex] and the value [tex]\( y = 0.8 \)[/tex], we need to determine the value of [tex]\( x \)[/tex].

1. Substitute the given value [tex]\( y = 0.8 \)[/tex] into the equation:

[tex]\[ 4x + 8(0.8) = 40 \][/tex]

2. Simplify the equation by calculating [tex]\( 8 \times 0.8 \)[/tex]:

[tex]\[ 8(0.8) = 6.4 \][/tex]

So the equation becomes:

[tex]\[ 4x + 6.4 = 40 \][/tex]

3. Isolate the term involving [tex]\( x \)[/tex] by subtracting 6.4 from both sides of the equation:

[tex]\[ 4x + 6.4 - 6.4 = 40 - 6.4 \][/tex]

[tex]\[ 4x = 33.6 \][/tex]

4. Solve for [tex]\( x \)[/tex] by dividing both sides of the equation by 4:

[tex]\[ x = \frac{33.6}{4} \][/tex]

[tex]\[ x = 8.4 \][/tex]

Therefore, the value of [tex]\( x \)[/tex] is 8.4.

The correct choice is:
[tex]\[ \boxed{8.4} \][/tex]