After substituting $t=2$, focus on evaluating $(0.4)^2$. Remember that an exponent of 2 means multiplying the base by itself.

Once you know the value of $(0.4)^2$, multiply that result by 5 to get $g(2)$, then match your result to the closest answer choice.

In Desmos, type 5*(0.4)^2 into an expression line. The numeric result that appears is the value of $g(2)$; compare that value with the answer choices and select the matching one.

The function is $g(t)=5(0.4)^t$ and we are asked for $g(2)$.

Substitute $t=2$ into the function:

Now compute $(0.4)^2$.

Remember that squaring means multiplying the number by itself:

So now we have:

Now multiply 5 by $0.16$:

So $g(2)=0.8$, which matches answer choice B.