Answer:
x represents the number of weeks of growth.
Step-by-step explanation:
Given: 
We are given a models the length (cm) of a lizard each week from beginning of the lizards life.
f(x) represents the length of lizards after x week
x represents the number of weeks from beginning.
Because it is a exponential growth function

where,


If b>0 then growth
If 0<b<1 then decay
x represents the time of decay or growth.
So, In the given equation x represents number of weeks of growth because b=1.24 >1