Tasks not in appropriate parent element

[siwelwerd]

Seeing this warning building the Calculus:

warning: * PTX:DEPRECATE: (2017-08-04) the "task" element is no longer used as a child of a top-level division, but is instead being used to divide the other "project-like" elements.  It can be replaced by a functional equivalent: "project", "activity", "exploration", or "investigation" (4 times)
*              located within: "Sample Problem" (title)
*              located within: "Sample Problem" (title)
*              located within: "Sample Problem" (title)
*              located within: "Sample Problem" (title)
* --------------

It looks like the sample problem at the end of the new PS5 section needs to get wrapped up in a <activity> or something, the <task>s can't be children of a subsection