To solve this equation, we first need to simplify the expression on the left side of the equation:

(0.2x + 0.4x) * 3.5 = 6.3

Combine the x terms:

(0.6x) * 3.5 = 6.3

Now, multiply 0.6x by 3.5:

2.1x = 6.3

To solve for x, divide both sides of the equation by 2.1:

x = 6.3 / 2.1
x = 3

Therefore, the value of x that satisfies the equation is 3.