Determine the Equation of the Graph $s ( 0 ) = 6$

Determine the equation of the graph.
-Suppose that a weight on a spring has an initial position of $s ( 0 ) = 6$ inches and a period of $\mathrm { P } = 2.5$ seconds. Find a function $\mathrm { s } ( \mathrm { t } ) = \mathrm { a } \cos ( 2 \pi \mathrm { Ft } )$ that models the displacement of the weight.

A) $s ( t ) = 12 \cos ( 2 \pi ( 2.5 ) t )$
B) $\mathrm { s } ( \mathrm { t } ) = 12 \cos ( 2 \pi ( 0.4 ) \mathrm { t } )$
C) $s ( t ) = 6 \cos ( 2 \pi ( 2.5 ) t )$
D) $s ( t ) = 6 \cos ( 2 \pi ( 0.4 ) t )$