The titration formula is used when we have an equivalence point of neutralization between acid and base, the formula is:
Ma * Va = Vb * Mb
Where:
Ma = concentration of acid
Va = volume of acid
Mb = concentration of base
Vb = volume of base
This formula tells us the concentration and volume of an acid must be equal to the concentration and volume of a base in order to neutralize the reaction (this applies to strong acids and strong bases only)
Ma * Va = Vb * Mb
0.00100 * 27 = 225 * Mb
0.027 = 225Mb
Mb = 0.00012M