The answer is (5 + 6) x 7 - 3.
5 + 6 = 11. 11 x 7 = 77. 77-3 is 75.
You can figure this out through trial and error. For example, if you try to add all of the numbers together, you'll see that the result is much too small. This means you'll have to multiply at least once. So, the next step is figuring out what times what gets you close to 75, and so on.
