can someone please help me understand this question?

Thank You :-)

A certain preparation consists of liquids x, y, and z in the proportion 5:2:1. How many gallons of the preparation can be made from a stock of materials consisting of 25 gallons of x, 20 gallons of y, and 8 gallons of z?

A. 25

B. 40

C. 80

D. 53

E. 50