If P and Q have different non-zero dimensions, which of the following operations is possible ?

Two physical quantities P and Q have different dimensions. Which of the following mathematical operation is/are possible?

Two quantities A and B have different dimensions. Which of the following is physically meaningful?

If P, Q and Rare physical quantities having different dimensions, which of the following combinations can never be a meaningful quantity?

If P, Q and R are physical quantities having different dimensions, which of the following combinations can never be a meaningful quantity ?

If P, Q, R are physical quantities, having different dimensions, which of the following combinations can never be a meaningful quantity ?