First find the X and Y coordinates of each point M and O
M is located at x = 1 and Y = -2, which is written as (1,-2)
O is located at x = 7 and Y = 6, which is written as (7,6)
Using those two points and the distance formula sqrt((x2-x1)^2 +(y2-y1)^2) we can find the length:
MO = SQRT ( (7-1)^2 + (6-(-2)^2))
MO = SQRT (6^2 + 8^2)
MO = SQRT (36 + 64)
MO = SQRT (100)
MO = 10 units