Answer:
4 weeks
Explanation:
Step one:
ben has 72 followers on his first day.
He averages 10 new followers each week
let the number of weeks be x
and the total followers be y
y= 72+10x--------1
Sarah also started a Twitter account and
has 100 followers on her first day and averages
3 new followers each week
let the number of weeks be x
and the total followers be y
y= 100+3x--------2
Step two:
let us equate the two expression to get the number of weeks x
72+10x=100+3x
collect like terms
10x-3x=100-72
7x=28
divide both sides by 7
x=28/7
x= 4 weeks