1.56°23′48″+16°35′43″
=72°58′91″
=72°59′31″
2.90°-28°12′36″
=89°59′60″- 28°12′36″
=61°47′24″
3.12°34′乘以4
=48°136′
=50°16′
4.40°40′ ÷6
=36°276′240″÷6
=6°49′40″能再详细一点吗？