Your task is to create a function that does four basic mathematical operations.
The function should take three arguments - operation(string/char), value1(number), value2(number). The function should return result of numbers after applying the chosen operation.
basicOp('+', 4, 7) // Output: 11
basicOp('-', 15, 18) // Output: -3
basicOp('*', 5, 5) // Output: 25
basicOp('/', 49, 7) // Output: 7