To find the product of abc, we first need to find the values of a, b, and c using the given information.

Given that a:b:c = 8:5:6, we can set up the following equations:

a = 8x
b = 5x
c = 6x

where x is a common multiplier.

Since a + c = 42, we can substitute the values of a and c into the equation:

8x + 6x = 42
14x = 42
x = 3

Now that we have found the value of x, we can find the values of a, b, and c:

a = 83 = 24
b = 53 = 15
c = 6*3 = 18

Finally, we can find the product of abc:

abc = 241518 = 6480

Therefore, the product of abc is 6480.