=(4.2-2.4)÷4

= 1.8÷4

=0.45

( 15300÷600+67.5)× 180

=(25.5+67.5)× 180

=93× 180

= 16740

10500÷( 10500÷25× 1.25)

= 10500÷525

=20

[(5.84-3.9)÷0.4+0. 15] ×0.92

=[ 1.94÷0.4+0. 15] ×0.92

=5×0.92

=4.6

(2400-480×2.5)÷ 1.6

= 1200÷ 1.6

=750