Isadora bought 4 trees to plant in her backyard and spent no less than eighty-four dollars altogether. How many dollars could each tree have cost? Let t represent how many dollars each tree cost.
t is greater than eighty
t is greater than or equal to eighty
t is greater than twenty-one
t is greater than or equal to twenty-one

the question is: how much could EACH tree cost?
meaning you will have to divide 4t by 4 and also 84 by 4
this gives you:
\[\frac{ 4t }{ 4 } \ge \frac{ 84 }{ 4 }\]