Zoo tickets

One children's ticket to the zoo costs €3. One ticket for an adult costs €6. Aunt Kate and Uncle Jano went to the zoo with the children. Uncle Jano paid for all the tickets at the box office. Aunt Kate then gave him €15 for herself and all the girls. How much did Uncle Jano pay at the cash register if there were twice as many boys as girls?

Final Answer:

x =  39 Eur

Step-by-step explanation:

$$\begin{gathered} d=(15-6)/3=3 \\ c=2\cdot d=2\cdot 3=6 \\ x=6\cdot 2+3\cdot (d+c)=6\cdot 2+3\cdot (3+6)=39\text{Eur} \end{gathered}$$

Try another example