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]
