Math is done in certain accepted steps. Parentacees always come first, then you do multiplication and division before addition or subtraction. In the first example you do what is in the first and second parentaccess separarely then add them. Using the first parentacees first, you would divide 12/4 first since that is division and then add this (3) to 43. The second parentacess is similar. You multiply 6*4 then subtract 52 from it. The result is added to your calculation in the first parentacees.

The other problems are done the same way.