What is the common factor of the linear expression 81x+72?

What is the common factor of the linear expression 156x-39x-130?

What is the common factor of the linear expression $75x^3+10x^2+55x$ ?

What is the common factor of the linear expression 60x+22?

What is the common factor of the linear expression x+2x+3x?

What is the common factor of the linear expression $28x^{12}-56x^{13}$ ?

What is the common factor of the linear expression 21x^2+51x^2?