Trick to calculate these question fast.
10% of 550= 55
1% of 550= 5.5
To calculate 18% = 20% -2%
I.e 55*2 -11= 99
x% of 280= 143.8-99
x% of 280= 44.5
This eq can be solved easily or even we can do estimate
10% of 280= 28
5%of 280= 28/2= 14
1%of 280= 2.8
Adding them give you 44.8= 16%
Hence the answer is 16%