#4 _Mr. Black has _12,000 dollars_ invested. Part of this is invested at 6 percent, and the remaining part is invested at 8 percent. if the interest from the 6 percent investment is _230 dollars_ more than the interest from the _8 percent_ investment, how much is invested at each rate?

#5 _A total of _6,000_ dollars is invested, part of it at 8 percent and the other part at 12 percent. how much is invested at each rate if the annual rate is _620_ dollars?

#6 How many _liters_ each of a 40 percent _acid solution and a 55 percent acid solution must be used to produce _60 _liter of a _45 percent acid solution?

#7 A _dairy store needs _360 gallons of _milk containing 4 percent fat. How many _gallons each of _milk containing _5_ percent fat and milk containing _2_ percent fat must be used to obtained the _desired _360 _gallons?