The answer is option b. $58.56
Valma produced 168 units. For the first 100 she got paid $.30 per unit. For the 68 remaining she got paid $.42 for each unit.
Then:
100 units * $.3 = $30
68 units * $.42 = 28.56
Now we add up:
$30 + $28.56 = $58.56
Thus, option b is the right one.