To find the value of the expression 3x(2x+3) - (3x+2)(2x-3) when x=0.4, we first need to substitute x with 0.4 in the expression:

3(0.4)(2(0.4)+3) - (3(0.4)+2)(2(0.4)-3)
= 3(0.4)(0.8+3) - (1.2+2)(0.8-3)
= 3(0.4)(3.8) - (3.2)(-2.2)
= 1.14(3.8) - (3.2)(-2.2)
= 4.332 - (-7.04)
= 4.332 + 7.04
= 11.372

Therefore, the value of the expression 3x(2x+3) - (3x+2)(2x-3) when x=0.4 is 11.372.