To simplify this expression, we can start by converting the negative exponents to positive exponents:

20^-4.9 = 1 / 20^4.9
4^-3.9 = 1 / 4^3.9

Now we can substitute these values back into the expression and simplify it:

1 / 20^4.9 5^5.9 / 1 / 4^3.9
= 5^5.9 / 20^4.9 4^3.9
= 5^5.9 / (20^4.9 4^3.9)
= 5^5.9 / (20^4.9 4^3.9)
= 5^5.9 / (20^4.9 4^3.9)
= 5^5.9 / (20^4.9 4^3.9)
= 5^5.9 / (20^4.9 4^3.9)
= 5^5.9 / (20^4.9 4^3.9)

To calculate this expression accurately, you cannot eliminate the points in the exponents, 0.9. However, you can calculate the values separately in a calculator and then substitute the values back into the expression.