Let's begin by listing out the information given to us:
[tex]\begin{gathered} a=\frac{1}{4},b=6.16a \\ 16a^2-4b \\ \text{Substitute the values of a and b into the expression, we have:} \\ 16a^2-4b=16a^2-4(6.16a)=16\cdot(\frac{1}{4})^2-4(6.16a) \\ 16\cdot\frac{1}{16}-4(6.16\cdot\frac{1}{4})=1-6.16=-5.16 \\ \Rightarrow-5.16 \end{gathered}[/tex]