The new volume is 1.9 ml
calculation
The new volume is calculated using the combined gas equation
that is P1V1/T1 = P2V2/T2 where
P1= 1.0 atm
V1= 21 ml
T1 = 10.0 c into kelvin = 10 + 273 = 283 k
P2 = 15 atm
V2=? Ml
T2 = 120 c into kelvin = 120 +273 = 393 K
make V2 the subject of the formula by multiplying both side by T2/P2
V2=T2P1v1 / P2T1
V2=[(393 k x 1.0 atm x 21 ml) / (15 atm x 283 K)] = 1.9 Ml