1.8%=0.018
2.15%=0.0215
2.35%=0.0235 then
0.018+0.0215+0.0235=0.063
here we have to find average of 3.so,0.063/3=0.021

Or;

1.8+2.15+2.35=6.3
& 100+100+100=300
so,6.3/300=0.021

EDIT by mod: Your second approach was wrong and I corrected it. You had already divided by 300 (the total), so why divide by 3 again? Your first answer was already good.

1.8% + 2.15% + 2.35% = ? Divided by 3 = ?%