How many crotchets equal a semibreve tied to a dotted minim?

Semibreves cannot be tied to dotted minims. In any case, a semibreve is worth 4 crotchets and a minim is worth 2, but a dot adds half the value of the note to the note, so a dotted minim is worth 3. The answer to your question is 7 crotchets but it is not possible.