Step 1 :Given the mass (m) is 300g and the specific heat (c) is 0.09 cal/g°C.
Step 2 :The thermal capacity (C) of a substance can be calculated using the formula: C = m * c.
Step 3 :Substitute the given values into the formula: C = 300 * 0.09.
Step 4 :Calculate the result: C = 27.0 cal/°C.
Step 5 :\(\boxed{27 \, \text{cal}/{}^\circ \mathrm{C}}\) is the thermal capacity of the substance.