Given,

First term, a = 10

Common Difference, d = 6 - 10 = - 4(a₂ - a₁)

Using the formula,

Where S_n is the sum of first n terms

n = no of terms

a = first term

d = common difference

S₁₆ = (16/2)[ 2(10) + (16 - 1) (- 4)]

= 8(20 - 60)

= - 320