One-piece 6233

If we take six pieces, we will pay only for four. One-piece cost 7, and my mother bought 31 pieces. How much did she pay for the purchase?

Correct answer:

x =  147

Step-by-step explanation:

$$\begin{gathered} a=\lfloor 31/6\rfloor =5 \\ b=31-6\cdot a=31-6\cdot 5=1 \\ x=7\cdot (4\cdot a+b)=7\cdot (4\cdot 5+1)=147 \end{gathered}$$

Try another example