Exactly the way you did when you asked the question. Well done, you got it right.
70 = seventy
The correct spelling is seventy (70).
It is seventy-two
90th is written in word form as "ninetieth".
Seventy-six is the correct way to spell it.
$77.00 seventy-seven dollars
Setenta
Seventy
Seventy thousand
Seventy two
Seventy billion
two hundred seventy eighttwo hundred and seventy eight