The area of a parallelogram is ...
A = bh
Substituting the given values, you have
A = (3x +5)(7x -1)
We presume you want the product multiplied out. Use the distributive property for that.
A = 3x(7x -1) +5(7x -1)
A = 21x² -3x +35x -5
A = 21x² +32x -5
The area of the parallelogram is 21x² +32x -5.