Loan repayment with lump sum payment after 5 years

Beer induced query follows.

What have you done so far?
When I do part (a) I get 106.23 months which means that he’s going to pay for 107 months, while in the answer they provided it says 101 months
I calculate total payments after 5 years plus the lump sum
Then I subtract that from the total amount to be paid after 20 years without lump sum
Then divide the answer by the monthly payment to find the number of months he still needs to pay off the loan
 
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