Target question: what percent of the company's employees contribute at least 5% of their salary to the Charity Fund?
For an employee to contribute 5%, the employee has been part of those that contributed at least 4%.
Employees that contributed 5% < employees that contributed 4%
Statement 1: 20% of the company's employees contribute at least 4% but less than 5% of their salary to the Charity Fund.
$$Total\ employees\ that\ contributed\ge4\%\ =\ \left(employees\ that\ contributed\ 4\%\le x<5\%\right)+\left(employees\ that\ contributed\ge5\%\right)$$
Therefore, 25% = 20% + x
x = 25 - 20 = 5%
5% of total employee contributed at least 5% of their salary to charity fund. Statement is therefore SUFFICIENT.

Statement 2: 95% of the company's employees contribute less than 5% of their salary to the Charity Fund.
We can say that;
Total employee = (employee that donates > 5%) + (employee that contributes < 5%)
100% = x + 95%
x = 100 - 95 = 5%
5% of the total employee contributed at least 5% of their salary to charity funds. Statement 2 is SUFFICIENT.
Since each statement alone is SUFFICIENT. Answer = option D