TypeError: Function <function <lambda> at 0x00000195D80C6048> must return a DataFrame when passed to `Style.apply` with axis=None code example

Example: pandas apply function to each row lambda

def EOQ(D,p,ck,ch):
    Q = math.sqrt((2*D*ck)/(ch*p))
    return Q
ch=0.2
ck=5
df['Q'] = df.apply(lambda row: EOQ(row['D'], row['p'], ck, ch), axis=1)
df