Please help me understand the following question. The available solutions in Chegg for this question is not that good. Please explain in layman's terms.

The following Little Man program is supposed to add two input numbers, subtract a third input number from the sum, and output the result, i.e., OUT = 1 N 1 + 1 N2-1 N3 mailbox mnemonic code numeric code 01 02 03 04 05 06 07 08 901 399 901 199 399 901 299 902 STO 99 ADD 99 STO 99 SUB 99 OUT COB What is wrong with this program? Modify the program so that it produces the correct result