Mother bought me two toy balls.

US$ per 4 yuan.

Bought me another toy car.

12 yuan

Mother gave it to cashier 50 yuan.

How much should I get back?

50-(2×4+ 12)=30

Is this ok?

The second stage has contact support.

If you think the calculation in brackets is a little difficult

You can make it easier.

Xiaoming has four boxes of books.

5 copies per box

Lend Xiaohong 9 books.

How many books does Xiao Ming have after lending?

4×5-9= 1 1