looks like differentiation. without going into the reasons why, when you differentiate a term in the form
[tex]a \times {x}^{b} [/tex]
it turns into
[tex]a \times \frac{ {x}^{b - 1} }{b} [/tex]
as a hint you could rewrite the original term as
[tex] \frac{1}{4} \times {t}^{4} [/tex]
