What reasons does Antonio give Bassanio for not being afraid of the contract?

I assume that you are asking about what happens in Act I,
Scene 3.  In that scene, Antonio makes the deal with Shylock where Antonio will borrow
money to help Bassanio.  If he can't pay it back, Shylock can have a pound of his
flesh.  Bassanio worries about this, but Antonio basically just laughs at his
fears.

Antonio gives one major reason for dismissing
Bassanio's fears.  He says that there is plenty of time left before the money has to be
paid back and that his ships will be back a month before the loan is due.  He is saying
that, when his ships come back, he will have plenty of money and there will be no danger
of having to give up the pound of flesh.  There are two quotes that show
this:

Why,
fear not, man, I will not forfeit it;
Within these two months,—that's a month
before
This bond expires,—I do expect return
Of thrice three times
the value of this
bond.

and

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Come on; in this there can be no dismay,

My ships come home a month before the
day.