Let w be the number of white hydrangeas in the first bed and p be the number of pink ones.
Then
w + p = 45 1st bed so p = 45 - w
2w + 3p = 120 2nd bed or 2w +3(45 - w) = 120 so -w + 135 = 120 or w = 15
Since p = 45 - w then p = 30
Total number of whites = 3w = 45
Total number of pinks = 4p = 120
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