hi, you just have to invert the formula that you wrote:
this is the correct way:
total=height*length;
so what happens here is that, the height and length's value is multiplied and then is assigned to total or stored in the float variable total. What you wrote above will give you an error because it expects a variable at the left side to be assigned a value.
So you want to store the value in total so the correct way is the one i wrote above.