The cycle of unit digits of 7 is 7, 9, 3, 1 (7^1 = 7, 7^2 = 49, 7^3 = 343, 7^4 = 2401, 7^5 = 16807 and so on)
The cycle of unit digits of 3 is 3, 9, 7, 1 (3^1 = 3, 3^2 = 9, 3^3 = 27, 3^4 = 81, 3^5 = 243 and so on)
56 is divisible by 4 so unit digit of 87^56 is 1
43 divides by 4 has remainder 3, so unit digit of of 93^43 is 7
A = 1 + 7 = 8 > B = 1 * 7 = 7
=> A