Answer:(a)400min
(b)EZ plan
Explanation:
Given
For EZ plan cost $0.15 per minute
and Go Plan cost $40 + $0.05 per month
so for t minutes in a month both plan cost equals when
0.15t=40+0.05t
0.1t=40
t=400 minutes
for 400 minutes both cost equal.
(b)For 200 minutes
EZ plan cost

GO plan costs

So for 200 minutes we can use EZ plan