Need the algebraic equation using 1 variable

Question

You inherit $70,000 with the stipulation that for the first year, the money must be invested in two stocks paying 4% and 10% annual interest respectively.  How much should be invested at each rate if the total interest income earned for the year is to be $4000? (algebraic form using only one variable)

Answer 1

Invest x at 4% and 70000-x at 10%

 

4000=.04•x + .1•(70000-x)

 

multiply by 100 to eliminate the decimal 

 

400000=4x+10(70000-x)

6x=300000

x=50000

 

investing 50000 at 4% earns $2000

 

investing 20000 at 10% also earns $2000