We can solve this question by step deviation method.
First we have to construct a table with given details as shown in video.
We know, `Mean(barX) = A+(sumf_iu_i)/(sumf_i)**h`
As per table in video,
`A=70,sumf_iu_i = -2,sumf_i = 35 and h = 10`
`Mean(barX) = 70+((-2)/35**10) = 486/7=69.429`