Specifically for your case the answer of friend Everson is the one that answers your question.
But the Mysql client can also perform some operations with some additional level of complexity.
Examples:
SELECT (NFValIcmsSubs - NFValFCP)*2 as NFValIcmsSubs FROM TABELA
SELECT (NFValIcmsSubs - NFValFCP)*(FValIcmsSubs + NFValFCP) as NFValIcmsSubs FROM TABELA
As with basic arithmetic calculus operations, Mysql also has precepts between operators.
Thus, the multiplication and division operators are considered before the addition and subtraction operators.
If two operators have the same priority, the expression is read from left to right.
Use parentheses to force prioritization and to improve readability of expression.