Answer:
180
Explanation:
Using the ratio flats : bungalows = 10 : 3
Given there are 30 bungalows then dividing by 3 gives the value of one part of the ratio.
30 ÷ 3 = 10 ← value of 1 part of the ratio, thus
10 parts = 10 × 10 = 100 ← number of flats
Using the ratio houses : flats = 9 : 5
The number of flats = 100 thus dividing by 5 gives
100 ÷ 5 = 20 ← value of 1 part of the ratio, thus
9 parts = 9 × 20 = 180 ← number of houses