the picture in the attached figure
we know that
total boys=50+30+20------> 100
total girls=50+80+70------> 200
total chldren=total boys +total girls---------> 100+200-----> 300
number of boys who like the Simpsons=20
number of girls who like the Simpsons=70
number of children who like the Simpsons=20+70-----> 90
What percent of all children like the Simpsons?
P=number of children who like the Simpsons divided by total children
P=90/300------> 0.3 (30%)
the answer is
0.3