Answer:
0.0176
Explanation:
This is binomial distribution probability with formula:

Where
n is the total number of trials [here 15 properties]
p is probabilty of success, sell [p = 0.5]
r is what we want [here we want probability of selling less than 4 properties, so r = 4]
Less than 4 means r<4, which means r = 0, r=1, r=2, r=3
We use the formula above and put in 4 different values of r and sum up the result. We will use a binomial calculator online to make it easy. So:
+
+
+

This is equal to 0.0176