We set up the function P(d) where d is the number of days sine she started losing plants:

P(d) = Initial plants * (1 - Loss percent / 100)^d

Plugging in our numbers, we get:

20 = 150 * (1 - 4/100)^d

20 = 150 * (1 - 0.04)^d

Read left to right so it's easier to read:

150 * 0.96^d = 20

Divide each side by 150, and we get:

0.96^d = 0.13333333333

To solve this logarithmic equation for d, we type it in our search engine and we get:

d = 49.35

The problem tells us to round up, so we round up to

**50 days**