# Defining the results
Results =[["Harry",20,25],["Sandra",10,12],["Michelle",23,21],["Mike",18,16]]

#Adding the two test scores and appending them onto each persons list
Results.insert(lambda [x][3],result[x][1] + result[x][2])

#Printing the result to check the insert worked
print(Results)
#

↓
Results.insert(lambda [x][3],result[x][1] + result[x][2])