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First five multiples of 3 are

3, 6, 9, 12, 15

First term a = 3

Second term t₁ = 6

Third term t₂ = 9

Common difference d = t₂ – t₁ = 9 – 6 = 3

Thus, By using sum of n^th term of an A.P. we will find it’s sum

Where, n = no. of terms

a = first term

d = common difference

S_n = sum of n terms

We need to find S₅

Thus, correct answer is (A)