The scale factor is 1.5, which means that the revised chamber is larger. The new dimensions are just the old dimensions times 1.5.
The volume of the revise chamber is:
V = (1/3) (PI) [(D/2)^2] (H)
= (1/3) (PI) {[(5.7)(1.5)/2]^2} [(12)(1.5)]
= 344.4874 in3