Michelle borrows a total of $$4500$ in student loans from two lenders. One charges $3\mathrm{.}8\%$ simple interest and the other charges $6\mathrm{.}8\%$ simple interest. She is not required to pay off the principal or interest for $4yr.$ However, at the end of $4yr,$ she will owe a total of $$864$ for the interest from both loans. How much did she borrow At $3$:$8\%$ interest