To solve this question, you would need to uncover the equation behind that pattern.1 -> 3 -> 6 -> 10In this case, this is a triangular pattern which the equation for the amount of dots in a triangle is:n(n+1) / 2n represents the pattern no.Let’s test this out1(1+1) / 2 = 1(2) / 2 = 2 / 2 = 12(2+1) / 2 = 2(3) / 2 = 6 / 2 = 33(3+1) / 2 = 3(4) / 2 = 12 / 2 = 64(4+1) / 2 = 4(5) / 2 = 20 / 2 = 10As you can see, this equation holds up.To find r, you would need to make another equation with info provided from the question as such:r + 3 sequence - r sequence = 126To translate it into a math equation you do as such, since you know the equation, you can easily replace n with r or r + 3, so:(I shown in pic)