Lisa invests $4,000 in two types of bonds, bond a and bond b. bond a offers a 10% return, and bond b offers a 6% return. lisa invests $x in bond a and $y in bond b. her total return on the investment is $340. the system of linear equations defining the situation is (blank) . the amount lisa invested at the rate of 10% is , and the amount she invested at the rate of 6% is (blank) .