So "mogę" instead of "umiem" won't work here?
It is about the ability you have learned, so "umiem"
"Can" is about ability, not about learning.
"Can" is about an acquired ability in this case. That's what immery meant by "have learned".
What part of the English phrase indicates that it is about acquiring the ability (by learning) and not about temporary physical condition, for example?
To me both 'umiem' and 'mogę' should be considered as correct. Do Duolingo algorithms allow multi choices?
Do "rachować" and "liczyć" mean the same?
Rachować means to calculate, to do calculations, to do (the) math(s). The dictionary refers to it as 'dated'.
Some nights I should not be doing this, this is one of them.