Question 215952
For now, Mark is 2/3 of Helen, so let us say Mark is 2x, therefore Helen is 3x.

In seven years, 2x+7 = 3(3x+7)/4 or 4(2x+7) = 3(3x+7)

Giving 8x+28 = 9x+21

Solved gives x = 7

Let us test it:

Now: Mark is 14 and Helen is 21 (two thirds of  21 = 14)

Add 7: Mark will be 21 and Helen will be 28 (21 is three quarters of 28)