Hi Thomas, I gathered some partial screenshots for a couple of the specific examples you gave. below are the URLs.

http://www.wolframalpha.com/input/?i=solve+3x-4%3D6

http://www.wolframalpha.com/input/?i=convert+43%2F4+to+a+mixed+number

Thanks for the question, Peter

Attachments:

As indicted in responses, Wolfram|Alpha can be used for the requested purpose. I want to mention that there is also some amount of material at demonstrations.wolfram.com, with some classified by US curriculum standards.

http://demonstrations.wolfram.com/ccss-explore.html

There is a coarser classification for math and some other areas that can be found as follows.

(1) Near bottom of page for demonstrations, under "Browse Topics", click on the "pi" symbol next to "Mathematics" (2) This takes one to the page http://demonstrations.wolfram.com/topics.html?Mathematics#2 Click on icon near top, to the left of "School Mathematics" (3) This opens a set of categories, amongst them "Middle School Mathematics", "Elementary School K-2 Mathematics", "Integers", Pre-Algebra", maybe 24 in all. Click on any to get relevant Demonstrations.

I do not claim that all of them will be relevant, but I believe there is a fair amount of useful work for purposes of math education at the levels under consideration.