To solve this equation, we first need to simplify both sides of the equation separately.

First, let's simplify the left side of the equation:
3(6x+15) - 8(10x+56)
= 18x + 45 - 80x - 448
= -62x - 403

Now, let's simplify the right side of the equation:
6(7x-105) - 165
= 42x - 630 - 165
= 42x - 795

Now, we have the simplified equation:
-62x - 403 = 42x - 795

Next, we need to isolate the variable x on one side of the equation. Let's first add 62x to both sides of the equation:
-62x + 62x - 403 = 42x + 62x - 795
-403 = 104x - 795

Next, let's add 795 to both sides of the equation:
-403 + 795 = 104x - 795 + 795
392 = 104x

Finally, we can solve for x by dividing both sides by 104:
392/104 = 104x/104
4 = x

Therefore, the solution to the equation is x = 4.