In the arthmetic sequence, the first term is 3 and the fourth term is 12. Find the common difference (d) and the sum of the first 10 terms.
a. Finding dun = u1 + (n-1)du4 = u1 + (4-1)d12 = 3 + 3dd = 3
b. Sum of first 10 termssn = n/2(2u1 + (n-1)d)s10 = 5(6 + 9d)s10 = 30 + 45(3)s10 = 165
