You have to use quotes to define a string and they don't need when you're using integers.
>>>"2" -> string
>>> 2 -> integer.
, arithmetic operations are done using integers.
Another thing that you need to consider in arithmetic operations is operator precedence. It's something called "PEMDAS" in python(BODMAS in Mathematics). According to that, 1+2*3 returns 7 instead of 9. The reason that it returns 7 is because * operator has higher precedence than +. But, you can use parenthesis to handle this case since it has higher precedence than other operators. Hence, (1+2)*3 returns 9.
Your question says that multiply the sum of 5 and 6 by 57.3 meaning, you have to get the sum of 5 and 6 before multiplying them by 57.3.