rectangular wooden block is 5 cm long, 3 cm wide, and a cm high. After its surface is painted red, all sawn into small cubes with a side length of 1 cm. Among these cubes, there are 15 cubes that are not painted red, how many small cubes are painted red?
一个长方形木块，长5厘米，宽3厘米，高a厘米．将它的表面涂上红色后，全部锯成棱长是1厘米的小立方体．在这些立方体中，没有被涂上红色的立方体有15个，那么涂上红色的小立方体有多少个．
<gadget id="calculator">15 * 7</gadget>
<output>105</output>

<gadget id="calculator">105 - 15</gadget>
<output>90</output>

<result>90</result>