Calculating with Symbols

& x & = €&
What is &?

Each Symbol is one Number.
Possible answers: 0, 3 , 7 , 6

Correct answer: $6$, because $6 \times 6 = 36$

What is the correct name of this kind of Puzzle?
Where can i get more of these?

In Germany we use them in Aptitude Tests.

• Welcome to Puzzling! (Take the Tour!) Has a correct answer been given? If so, please don't forget to $\color{green}{\checkmark \small\text{Accept}}$ it :) – Rubio Aug 16 '17 at 23:17