How much meat do you want?（你想要多少肉?）
How much beef do you want?（你想要多少牛肉?）
How much of this beef do you want?(你想要多少两肉?)
HOw much of this meat do you want?(你想要多少两牛肉?)
下面两句听起来更正规, 而且一般来说是对方先跟你说他想买牛肉,所以正常是应该用(你想要多少两肉?)才对.
by雁子~