8
225 (base n)=(2*n*n+2*n+5) 2n^2+2n+5=149 solving this we get n=8
225 in base n = 2×n^2 + 2×n + 5 = 149 in base 10 2n^2 + 2n + 5 = 149 2n^2 + 2n - 144 = 0 n^2 + n - 72 = 0 n^2 + 9n - 8n - 72 = 0 n×(n + 9) - 8(n + 9) = 0 n - 8 = 0 n = 8.