To solve this equation, we first need to convert the mixed numbers into improper fractions:

13/4x - 39/12 * 21/5 = 0.4

Next, we need to simplify the fractions:

52/20x - 39/12 * 21/5 = 0.4

52/20x - 273/60 = 0.4

Multiplying both sides by 60 to eliminate the fraction:

60 (52/20x) - 60 (273/60) = 0.4 * 60

This simplifies to:

156x - 273 = 24

Adding 273 to both sides:

156x = 297

Dividing by 156:

x = 297/156

x ≈ 1.904

Therefore, the value of x that satisfies the equation is approximately 1.904.