Label the cards A, B, C from smallest to largest value.
B is in the middle. Because the median is 4, we know that B = 4.
The cards A, B, C can be updated to A, 4, C
We cannot determine A nor C. There isn't enough information. However, we do know that C-A = 3 because the range is the difference of the max and min.
The equation C-A = 3 can be solved to C = A+3.
Here are some example sets of trios we could have
A = 2, B = 4, C = 5
A = 3, B = 4, C = 6
We cannot have A = 4 as this would start to step on B. I'm assuming the cards display different values.
Notice that A = 1 isn't possible because C = A+3 = 1+3 = 4, which also steps on B.