Help with calculating errors and slope in Fortran 90.

great_sushi

Writing a fortran program to find errors in a and b?
I am writing a program to calculate the y-intercept, best slope and the errors in a and b. I have been able to write up until the errors, which is where im struggling. This is what i've done so far:

PROGRAM assignment4
IMPLICIT NONE
INTEGER :: i,n
REAL :: sumx, sumy, sumxx, sumxy, a, b, e, f
REAL :: sumax, sumb, sumyi, sumd
REAL :: x(100),y(100)
!
PRINT*,"How many points to be entered(Max 100)?"
READ*,n
PRINT*,"Enter the data pairs,x,y"
!
DO i=1,n
READ*,x(i),y(i)
ENDDO
!
Sumx=0
Sumy=0
Sumxx=0
Sumxy=0
!
DO i=1,n
Sumx= sumx+x(i)
Sumy= sumy+y(i)
Sumxx= sumxx+x(i)**2
Sumxy= sumxy+x(i)*y(i)
ENDDO
!
a=(sumxy-sumx*sumy/n)/(sumxx-(sumx*sum