M點(diǎn)高程Hm=43.251m,測(cè)得后視讀數(shù)a=1.000m,前視讀數(shù)b=2.283m。則N點(diǎn)對(duì)M點(diǎn)的高差hMN和待求點(diǎn)N的高程HN分別為:()