.
Let x be the amount to invest at 12.2%, in dollars.
Then the amount to invest at 5.4% is (50000-x) dollars.
The total interest is the sum of partial interests.
It gives you an equation
    0.122x + 0.054*(50000-x) = 4300  dollars.
From the equation, express "x" and calculate
    x =  = 23,529.41.
ANSWER.  $23,529.41  should be invested at 12.2%;  the rest,  (50,000 - $23,529.41) = $26,470.59 should be invested at 5.4%.
 = 23,529.41.
ANSWER.  $23,529.41  should be invested at 12.2%;  the rest,  (50,000 - $23,529.41) = $26,470.59 should be invested at 5.4%.