Ken contracted with Larry to mow his lawn once a week for one year for $25 per week. The written contract stated that "Ken will mow Larry's lawn once a week, for one year, at a rate of $25 per week." Last year, Ken had also contracted with Larry to mow his lawn under the same contract terms as listed above, and Ken mowed Larry's lawn and also trimmed Larry's bushes every week for the same rate of $25 per week. For the first three months (or 12 visits) of this year, Ken also trimmed Larry's bushes. Upon the next visit, Ken mowed Larry's lawn but stopped trimming the bushes, Larry refused to pay Ken because Ken did not complete the job by not trimming the shrubs. Does Larry have to pay Ken? Explain? Is Ken obligated to also trim the shrubs? Explain