Beer Burger Math Equation Puzzle

The answer of the obove equation is 15.

Explaination:

Let the bottle be, B

the burger be, BU

& Let the Glass of alcohol be, G

Rewriting the equations in the form of the above terms.

Equation (1); B + B + B = 30

Equation (2); B + BU + BU = 20

Equation (3); BU + 2G + 2G = 9

Equation (4); BU + G * B =?

Solving equation (1);

B + B + B = 30

3B = 30

B = 10

Putting B, in equation (2);

B + BU + BU = 20

10 + 2BU = 20

2BU = 10

BU = 5

Now, substitute the value of BU in equation (3);

BU + 2G + 2G = 9

BU + 4G = 9

5 + 4G = 9

4G = 4

G = 1

Now put the value of G, B & BU in final equation (4);

BU + G * B =? 

= 5 + 1 * 10

= 15

BU + G * B =15