An AE student named Seoung devises a coded system of arithmetic for keeping his financial information private. His coded system of arithmetic is identical to the usual one except that each digit 0 to 9 has a value different than from standard arithmetic.
The following five equations hold in Seoung's arithmetic:
(a) 8×7 = 8
(b) 4×9 = 39
(c) 7-33 = -1
(d) 51÷2 = 2
(e) 7^4 = 6.
What is the sum 40 + 04 in Seoung's arithmetic expressed in his new digits?