Whenever you want to replace the ⊗ operation with its answer.
If you have the symbol x in any expression, you replace the x symbol with its answer. For instance, when the expression is 4 + 6 x 5, you simplify it by replaceing 6 x 5 with 30, giving you 4 + 30, which is 34.
So, if you have the expression 4 + (49 ⊗ 2 ), you calculate 49 ⊗ 7 to be √49 + 2 = 7 + 2 = 9.
Then, you have 4 + 9 = 13.