Multiplication problem solving

Last week Jackson's Studio (room 18) were learning how to do maths problem solving with multiplication.

The question was: 
"The 4 Legend classes each had 42 children attend(a few children obviously invited their cousins), how many attended the disco altogether?"

I used the strategy of place value

4x42=? 
4x2=8
4x40=160
160+8=168

That's how I got the answer.