Im in desperate need and I'm stuck: Can someone plsease tell me where I'm going wrong with this question.

Calculate the sample correlation between test score and assembly time.
Test Score Assembly Time (minutes)
(x) (y)
40 16
50 14
60 12
75 10
80 8
85 10
90 7
---------------------------------------
540 77
MY WORK:
X^2=1600,2500,3600,5625,6400,7225,8100=35050
y^2=256,196,144,100,64,100,49=909
X*Y=640,700,720,750,640,850,630=4930

ss(xy)=4930-(540*77/7)=-1010
ss(x)=35050-(291600/7)=-6607.142
ss(y)=909-(5929/7)=62

Correlation Coefficient is:
r=-1010/(square root of -6607.142 * 62)=??

This is where I get stuck. Every time I try to calculate the answer I come up with an error. Can someone tell me if I did this correctly. I can't seem to get the answer to the coefficient

In your final calculation, you are trying to find the square root of a negative number, which is a definite no-go, there is no such real number!
I think that's probably what's causing the error to occur. It would seem as though you're value for ss(x) is incorrect, I think it should be:

35050 - (230 400 / 7) = 2135.714

Chances are you have probably added up the figures for ∑(x) incorrectly.

Just seen the date on this question! Oh well, hope it helps someone!

Input your data in spss and get your correct answer. If you want to do it manually it is also possible but you have to be very careful to avoid simple mistakes.