An experiment is conducted for infiltration rate under the ponding condition in a soil field and it follows the Horton’s equation. Infiltration rate in the beginning of the experiment was 25 cm/h. If the infiltration rate after 5 hours reduced to 15 cm/h and the Horton’s decay constant is 0.18 hr^-1, then the infiltration rate after two hour of the start of the experiment is ________ :