You can round 406to420 then divide by 7 or 406-490 divided by 7
Answer:
15b + 30
Step-by-step explanation:
By expansion (6 x 2.5b) + (6 x 5)
= 15b + 30
Mixing the two concentrations would give a new concentration which is in between 50 - 60% .
D. 63% cannot be obtained