أولاً نبسّط الأساس: (23+3) = 26. Reduce it modulo 7: 26 ≡ 5 (mod 7). The powers of 5 modulo 7 repeat in the cycle 5, 4, 6, 2, 3, 1. Since exponent 28 points to the cycle value 2, 26^28 leaves remainder 2.