80:8+5×15-49÷7=
=10+75-7
=85-7
=78
54÷9+20×6+72÷9=
=6+120+8
=126+8
=134
100-63÷7+52×4=
=100-9+208
=91+208
=299
420+25×8-100÷10=
=420-200-10
=220-10
=210
