90÷﹙3.6-1.8﹚
=90÷1.8
=5
3.4×7.8÷3.9
=3.4×2
=6.8
5.23×4+4.77÷0.25
=5.23×4+4.77×4
=4×(5.23+4.77)
=4×10
=40