To solve this equation, we can first simplify the expression (17/20x - 1.72)/1.3 to make it easier to work with.

Dividing the numerator by 1.3, we get:
(17/20x - 1.72)/1.3 = (17/20x - 1.72) * (1/1.3) = 0.45x - 1.32

Therefore, our new equation is 0.45x - 1.32 = 2 3/5.

Next, we need to simplify 2 3/5 to an improper fraction:
2 3/5 = (2*5 + 3)/5 = 13/5

So our equation becomes:
0.45x - 1.32 = 13/5

Now, we can solve for x:
0.45x = 13/5 + 1.32
0.45x = 13/5 + 1.32
0.45x = 13/5 + 1.32
0.45x = (13 + 5*1.32)/5
0.45x = 19.6/5
x = (19.6/5) / 0.45
x = 3.46

Therefore, the solution to the equation (17/20x - 1.72)/1.3 = 2 3/5 is x = 3.46.