Determine the concentration of this acid

Determine the concentration of an unknown (monoprotic) acid if 25.0mL of 0.100mol/L Ca(OH)2 is required to completely neutralize a 15.0mL sample of the acid.

Can anyone show the steps to completing this problem? I tried it but don't know if I have the right answer or not. :/

Monoprotic acid donates 1 proton per molecule. I will assume it is a strong acid and will dissociate completely in water.
Note that Ca(OH)2 donates two hydroxide per molecule. Therefore each molecule of Ca(OH)2 can neutralize two molecules of the acid.
It then follows that 1 mole of Ca(OH)2 neutralizes two moles of acid.

A good place to start is to find out how many moles of Ca(OH)2 we have:
0.100 mol/L x 0.025 L = 0.00250 mol Ca(OH)2
(Liters canceled out, yielding moles)

Double that to get the moles of acid neutralized: 0.00500 mol Acid
Concentration = mol/L
so divide moles of acid by liters (convert 15.0 mL)
0.00500 mol / 0.0150 L = 0.333 mol/L

molarity of acid times volume of acid = molarity of base times volume of base.

first you should know Molarity = moles of substance/liters of solution, so you need to convert the volume in terms of liters. then just solve the equation above for molarity of acid , then plug in.