Answer:
(b) 5.
Step-by-step explanation:
The bottom numbers are calculated from the 2 above them according to the formula:
c = 15(a + b)
- because: 75 = 15(2 + 3) and
165 = 15(7 + 4)
Therefore if the unknown number is x :
285 = 15(14 + x)
285 = 210 + 15x
15x = 285 - 210
15x = 75
x = 5.
