JS Calculator

I need urgent help on a calculator I'm working on, everything on the program seems work but it can't calculate the total.

What the program is suppose to do is:
Multiply - Block width by Block length - Works
Multiply - House width X House length - Works
Then from the calculations made above it will then display the total of both block and width - Works
But heres the problem, I want it to subtract the total made in both the block and house and multiply by 2.

Thanks in advance