What's Wrong With This?

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#Pneumatic Air Gun Calculations
import matplotlib.pyplot as plt

#Variables Outlined

#Muzzle Velocity
Vm=var('Vm')
#Atmospheric Pressure
Patm=var('Patm')
#Gas Chamber Volume
Vc=var('Vc')
#Barrel Area[Internal]
Ab=var('Ab')
#Barrel Length
Lb=var('Lb')
#Specific Heat of Air
k=var('k')
#CB Ratio[see table]
cb=var('cb')
#formula variable
eng=var('eng')
#2nd Formula Variable
eng2=var('eng2')
#Mass of the Projectile
md=var('md')
#Operating Pressure in atm
Pc=var('Pc')

#Definitions
k = 1.4
Patm = 101235
cb = 0.261208
#m/s^2
Vm= 91.44
md=2
Pc=10
eng=0.618081

#Main Formula
solve(eng=(k-1)*md*Vm^2/(2*Patm*Vc*(Pc-Pc^(1/k)),Vc)

Can anyone tell me why this is giving a syntax error and pointing to my variable definition Vm? It's really bugging me!