3.35% simple rate of interest on $50,000 earns [($50,000*3.35)/100]=$1675 in a year which is a part of $6000 that Lisa need per year all together
Hence the rest of the interest should be ($6,000-$1,675)=$4,325
The remaining capital = ($120,000-$50,000)=$70,000
Thus $70,000 can earn $4,325 at the rate of simple interest = [($4,325/$70,000)*100] ≈ 6.18
Therefore, Lisa would need on the rest, i.e., $70,000, 6.18 % interest rate in order to get $6,000 per year in interest all together.
NOTE: I calculated with simple rate of interest instead of compound interest rate because of the available data. The frequency of compounding was required to calculate compound interest rate, which has no mention in the question.