Let
y ----> total charge in a month
x ----> number of minutes
so
Plan A
y=0.21x+11
Plan B
y=0.10x+20
Equate both equations
0.21x+11=0.10x+20
solve for x
0.21x-0.10x=20-11
0.11x=9
x=9/0.11
x=81.82 minutes
Convert to hours and minutes
81.82 minutes=60+21.82=1 hour 22 min
therefore
the answer is option A
