Answer
... an increase by $ 2.5\%$ each year
Work Step by Step
Exponential growth and decay models are given by $A=A_{0}e^{kt}$
in which $t$ represents time,
$A_{0}$ is the amount present at $t=0$, and
$A$ is the amount present at time $t$.
If $k>0$, the model describes growth and $k$ is the growth rate.
If $k<0$, the model describes decay and $k$ is the decay rate.
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Nigeria's growth rate may mean the population growth, the growth of GDP, etc.
In any case, an exponential growth model is assumed.
By this model, the population (GDP...) of Nigeria shows
an increase by $ 2.5\%$ each year