180
How I got it:
10% of 900 = 900. to 90.0 (just move the decimal point over one place)
to get 20% just double the 10%
180
900 - 20% = 720
900-20 = 880
20%
It is 900+180 = 1080
20 percent off of 750 is 600.
900 x 20% = 900 x 0.2 = 180
900 - 135 = 765
900 - 35% = 585.00
£180
900
20 percent off 249 = 199.20