Question 861041
Already answered the first one, although the answer isn't pretty.

S = ½(a + an)n
S = ½(2a + (n-1)d)n
an = a + (n - 1)d

970 = ½(-18 + 115)n
970 = ½(97)n
10=n/2
n=20 terms
133 = (19)d
d=7 difference