Question

f. I cannot go to the concert. (forget/to buy tickets)
g. Mother is very tired. (clean/entire house today)
h. We do not know where he is. (not call back)​

Answer 1

So, assuming you're asking what I think you're asking...

f. I cannot go to the concert because I forgot to buy the tickets.

g. Mother is very tired because she cleaned the entire house today.

h. We do not know where he is because he didn't call back.

Hope I helped!