The question is, calculate E, when significance level is 0.05

The question is, calculate E, when significance level is 0.05, 
and  

I used Excel and typed =t.inv(0.025,df) to find t(a/2). And its answer was -2.22814.
Then, calculated E=2.22814*sqrt(s1^2/n1+s2^2/n2), 
But my answer was false somehow.
Could you tell me how I was wrong and how to solve the question?