Thank you for the opportunity to help you with your question!
a)As for the first expression ,it means that the percentage of houses with internet access 23 years after 1980 is exactly 55
b)the second expression represents that, the percentage of households with internet connections 4 years after 1980 is k, which is universal for constant, which may imply that the number has remained constant.
c)the third expression means that the percentage of household with internet connections 27 years after 1980 is exaCTLY 61 0R GREATER THAN 61 BUT NOT ANY LESS THAN 61
d)as for the last expression,it is meant to represent that the percerntage of households with internert connection17 years after 1980 added to the percerntege of households 21 year after 1980 is approximately equal to the percerntage of households with an internert connection 29 years after 1980
Please let me know if you need any clarification. I'm always happy to answer your questions.
Oct 13th, 2015
hope the explanation helps to understand the expressions