Question 976865
Formula = a(n)= a(1) + (n - 1) d
a(1) = -6  d = 2 
a(8) = -6 + (8 - 1)2
a(8) = -6 + 14
a (8) = 8

Find the Sum
a(1) = 5: n = 20: d = 8

a(n) = a(1) + (n - 1)d
a(20) = 5 + (20 -1)8 
a(20) = 5 + 152
a(20) = 157

Sum formula = S(n) = n( a(1) + a(n))/2
Now, let's find the sum:
s(20) = [20( 5 + 157)]/2
s(20) = 3240/2 = 1620
Both answers are 'b'
Hope this helps:-)