To get the result we can use proportion
10% -----------80
100% ---------x
Crossmultiply now
10*x=100*80
10x=8000 /:10
x=800 - its the answer
33.333% -----------21
100% --------------x
crossmultiply
33.33x=21*100
33.33x=2100 /:33.33
x=63 - its the answeer