(70+71+72+x)/4 is greater than or equal to 73
the average is all of the plants divided by the number of plants, which is 4. we don't know what the other plant has to be, so it is called x. The average has to be at least 73, so greater than or equal to 73
add them up to get (213 + x)/4 is greater than or equal to 73. then divide 213 and x separately by 4 to get 1/4x + 53.25 is greater than or equal to 73. subtract 53.25 from both sides to get 1/4x is greater than or equal to 19.75 then divide both sides by 1/4 to get x is greater than or equal to 79
