we have that
Let
y ----> total charge
x ----> number of hours
so
First-rate
y=65x+400 ------> equation 1
Second rate
y=95x+100 ------> equation 2
Equate equation 1 and equation 2
65x+400=95x+100
solve for x
95x-65x=400-100
30x=300
x=10 hours
therefore
the answer is
After 10 hours