Answer:
b) 0.0625
Step-by-step explanation:
x > 0, if not 4/x < 0
0 < 4/x < 6/7
0 < 28/x < 6
0 < 28 < 6x
0 < 4 2/3 < x
profit= 6. 00x - (30+2. 50x)