Answer:
216 boys
Step-by-step explanation:
450 students: 20% girls, 80% boys
450*20%=90 girls
450*80%=360 boys
Students having mobile phones: 40% (OF THE 90) girls, 60% (OF THE 360) boys
90*40%=36 girls
360*60%=216 boys
[We honestly don't need to care about the girls without mobile phones as they are only asking how many boys have mobile phones]
What question are you trying to ask?
You have steak Mac water or steak mac water, etc etc...
Hi..... the domain(D) will be:

Thanks... :)