To find the number of chaperones, you could find the total number of students that are going on the field trip and then break this number into groups of 8.
(158 + 139)/8
297/8 = 37.125
You will need a minimum of 38 chaperones for the 297 students. If there is any remainder(decimal) you will need an extra chaperone so the groups do not exceed 8.
