Explanation:
According to the question,
AB+BC=AC
2x+1+6x=81
8x+1=81
8x=81-1
8x=80
x=80/8
x=10
AC = AB + BC
81 = 2x + 1 + 6x
81 = 8x + 1
81 - 1 = 8x
80 = 8x
80/8 = x
10 = x
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