ValueError: matmul: Input operand 1 has a mismatch in its core dimension 0, with gufunc signature (n?,k),(k,m?)->(n?,m?) (size 4 is different from 1)

The above error occurs when i run the following code:

 z=df[['horsepower','curbweight','enginesize','highwaympg']] 
 lm.fit(z,df['price'])
 yhat=lm.predict(x)