Okun was a professor at Yale who studied relationship between unemployment and productivity. He observed that for the US,when unemployment rises by 1%, then GDP is expected to fall by 2%.
So when unemployment goes from 2% to 5%, the GDP will fall by (5-2)*2 = 6%
I got this by knowing that when unemployment goes up by 1% GDP would drop by a following 2%
In the question you asked above the unemployment rate goes from 2% to 5% this means that the unemployment will go up by 3% while the GDP drops 6%