1. Subtract7/9-(-13/18)=3/2?
2. divide -12/0= indeterminate form?
3. Perform the indicated operation this problem looks like a fraction 11-6/7-7=5/0 or undefined?
1. 7/9 - (-13/18) = 14/18 + 13/18 = 17/18 ≠ 3/2
2 & 3. -12/0 and 5/0 are undefined.
http://mathforum.org/dr.math/faq/faq.divideby0.html