Which choice is appropriate simplified form and restriction for the variable (x+3)(x+7)/3x+21

A3/x+7 (x ≠ -7)

Bx+7/3 (x ≠ -7)

Cx+3/3 (x ≠ -7)

D3/x+3 (x ≠ -3)

Please help and explain the answer too!