Write numbers in rectangles, write operations in circles.
 You have to enter all the fields on the left side of the equation.
 The equation must be correct. The value on the left side of the equal sign must be equal to the value on the right side of the equal sign.
 Do not forget: multiplication and division take precedence over addition and subtraction.
 Computer keyboard:
[+ plus, addition] [- hyphen, subtraction]
[x letter, multiplication] [: colon, division]
 The meaning of colors:
The correct number (or operation) in the correct spot.
The number (or operation) is in the equation but not in this spot.
The number (or operation) is not in the equation.