<p>It appears that the 151 … Sequence is calc 1-3 in four courses, while the 161 … Sequence is calc 1-3 in three courses. I am unsure of how their quarter system works so I do not know how long each course is.</p>
<p>I believe that their system will not allow taking 151 courses because he has taken a 16x course and may not allow the 162 meaning that he should repeat 161 (I agree with uc here). He could try adding 161 to see what happens.</p>