First, a can only be equal to 1 or 2. If a= 1, there is no number with the mantissa of 1 after multiplying by 4, so a=2.

So the mantissa of d*4 is 2, and d is only 3,8. D=8 because abcd times 4 equals dcba.

And because abcd is greater than 2000 (because a=2) and dcba is less than 9000(d=8), bcd

B can only be equal to 0, 1, 2, because a=2, so B is not equal to 2. If b=0 and c= (because the last digit is 8,4 * 8 = 32, 3 will be entered), the result is not equal to dcba, so b= 1, so c can be equal to 5,6,7.