First: Multiply 5 by the numbers 100, 30, and 7, and add them together.
Second: Multiply 100 by the numbers 400, 80, and 6. Multiply 30 by the numbers 400, 80, and 6. Multiply 7 by the numbers 400, 80, and 6. Add all the numbers together.
As a tip, if you ever learned the FOIL method for multiplying functions like (x + 3)(2x - 7) (it goes First, Outside, Inside, Last), then you could do the same when multiplying two two-digit numbers, except thinking of x as ten.
I was taught how to multiply multiple-digit numbers and do long division on paper when I was like, seven, and I've been doing it in my head ever since.