If 21a7 is divisible by 9, then which digit can replace the letter a in the 4-digit [3M] number 21a7?

The verbal translation for the difference of m and 7 increased by 15

Acone with volume 1350 m³ is dilated by a scale factor of 1/3. what is the volume of the resulting cone? enter your answer in the box. m³

Ihave a triangle with a 60 degree angle. lets use d for that angle. what are the values of e and f if d is 60 degrees? and what do you notice about the values of e and f?