Answer:
is the required inequality.
Step-by-step explanation:
Let x be the greatest number of text message that he can do,
And, According to the question,
The cost of one text message = $0.20
And, Initially the amounts he has = $10
But, after spending $4 the remaining amount he has = 10 - 4 = $ 6
Now, total cost of the x messages = 0.20 x dollar
Again according to the question,
⇒
⇒ 
Which is the required inequality.
By this we can say that he can do maximum 30 messages with the money he has.