The answer of the above equation is 43.

Explaination:

Let the pair of shoes be, S

Let the boy be, B

& The burger be, Bu

Converting the above equations in the form of the above terms.

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

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

Equation (3); 2Bu + 2Bu + B = 13

Equation (4); (0.5)S + (B + 2Bu + S) * Bu = ?

Now, solve equation(1);

S + S + S = 30

3S = 30

S = 10

Substitute the value of S, in equation(2)

B + B + S = 20

2B + 10 = 20

2B = 10

B = 5

Similarly, substitute B in equation(3);

2Bu + 2Bu + B = 13

4Bu + 5 = 13

4Bu = 8

Bu = 2

Now, substitute all the values for final equation(4);

(0.5)S + (B + 2Bu + S) * Bu = ?

= (0.5)10 + (5 + 2*2 + 10) * 2

= 5 + (5 + 4 + 10) * 2

(0.5)S + (B + 2Bu + S) * Bu = 5 + 19 * 2

(0.5)S + (B + 2Bu + S) * Bu = 43