Question 851459
the first 2 digit multiple of three is 12
the highest is 99

an = a1 + (n - 1)d
99 = 12 + (n - 1)3
87=3n-3
90=3n
n=30 multiples
S = ½(a1 + an)n
s=1/2(12+99)*30
s=15*111
S=1665