Multiplication Pyramid

This is my multiplication pyramid that I have done.On each layer we have to times the number's together with the numbers on the left and they write it on the top and then it goes like that on the other layers.I hope you like it.

This is my top 3 questions and how I solved it.

1.75 x 180=???

75 x 100=7500

75 x 80=6000

7500+6000=13500

2.180 x 48= ???

180 x 40=7200

180 x 8 =1440

7200+1440=8640

3.13500 x 8640=???

13500 x 8600=116100000

13500 x 40 = 540000

116100000+540000=116640000