Given that he borrows $3000 for 90days,
Therefore, the principal is $3000.
If the interest is 4% collected on the principal amount,
Hence, the interest will be
[tex]\begin{gathered} 4\text{ \% of \$3000} \\ \frac{4}{100}\times\text{ \$3000=\$120} \\ \therefore Interest\text{ = \$120} \end{gathered}[/tex]Therefore, the total amount he will owe after 90days will be
Amount = Principal + Interest
Amount= $3000 + $120= $3120
Hence, he will owe $3120 after 90days.
