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, 144, 72, 54, 9, 1d) 1, 11, 66, 99, 121, 121, 99, 66, 11, 1 4. How many solutions are there to the equation x1+x2+x3+x4=17, where x1, x2, x3, x4 are nonnegative integers? a) 380 b) 960 c) 1140 d) 22805. How many strings of 10 ternary digits (0