It's A = 2, B = 7, C = 11, and D = 13

I tried trial and error method. Where I randomly choose prime numbers.

But given the equations, should use the smallest prime numbers as possible.

So its gonna be :

2 (2+7+11+13) = 11(13-7) > 66 = 66
1 + 7(11) + 13 = 13 (7) > 91 = 91
2 + 11 = 13 > 13 = 13

All the equations are equal, which means the values are the solution. This is not a recommended method but is useful if you haven't have a choice.