3600" - 30' + 1800" = ...
12\frac{1}{2}21o
0o
2o
1o
3600" - 30' + 1800"
= (3600÷\div÷3600o) - (30÷\div÷60o) + (1800÷\div÷3600o)
= 1o - 12\frac{1}{2}21o+ 12\frac{1}{2}21o
= 1o