In the following problem, '=' stands for '÷' , '+' stands for '' , 'x' stands for '=', '' stands for '+' and '÷' stands for 'x'. Find the correct equation.
The difference between the ages of mother and son was 21 when mother's age was 43. If father is elder by 3 years to mother, what will be the difference between the ages of son and father when father attains 50 years?