calculate('1 + 2'); // string '3' will be returned
calculate('VI / III'); // return string 'II'
calculate('VII / III'); // return string II'
calculate('I + II'); // return string 'III'
calculate('I - II'); // return string '' (empty string) there are no negative numbers in the roman system
calculate('I + 1'); // an exception (error) will be returned throws Error different number systems are used at the same time
calculate('I'); // throws Error exception will be returned. string is not a mathematical operation
calculate('1 + 1 + 1'); // throws Error exception will be returned. the format of the mathematical operation does not satisfy the task - two operands and one operator (+, -, /, *)