Calling Math Wizards!! Hypothesis Testing Question?

[WhosThatGirl?]

Please help! I'm not sure of the null hypothesis which of course if its not right will throw everyhting else off. I think it is
Null hypothesis -- mean1 = mean2
ALternative hypothesis -- mean 1 =/ (not equal) mean 2

I believe this question would then be a two-tailed test and you would use the z-test?

Question:
The MBA department is concerned that dual degree students may be receiving lower grades than the regular MBA students. Two independent random samples have been selected. 100 observations from population 1 (dual degree students) and 100 from population 2 (MBA students). The sample means obtained are X1(bar)=84 and X2(bar)=87. It is known from previous studies that the population variances are 4.0 and 5.0 respectively. Using a level of significance of .10, is there evidence that the dual degree students are receiving lower grades? Fully explain your answer.