How would i calculate the moles using this equation?

Moles= concentration x volume (dm^3)

i have the following info

concentration of 1.0moldm^-3 which has been calculated using 15cm^3 (in part A of question)

the volume i have now is 25cm^3 for part b

i have been asked to use my concentration of 1.0moldm^-3 from part a

so how would i actually calculate the moles because the volumes are different there is a difference of 10cm^3

would i need to use two calculations or does it involve a subtraction

or would i simply multiply the 1 by 25/1000 although this seems wrong!

please help!

thank you!