G = # of grasses W = # of weeds T = # of trees. W = 2G -5 <<<---=== From the condition T = 2G + 3 <<<---=== From the condition G + W + T = 103 G + (2G-5) + (2G+3) = 103 ====================> 5G - 2 = 103, 5G = 103 + 2 = 105 ====> G == 21. From this point, can you complete the solution on your own ?