4. Determine if the following relation is a tree. If yes, identify the root and the height. If no, explain what condition is violated and provide an example.
a. A = {a,b,c,d,e,f,g,h}, R = {(g,f), (h,d), (c,e), (b,g), (c,a), (b,h), (g,c), (h, f)}
b. A = {a,b,c,d,e, f, g, h, i}, R = {(e,g), (c,b), (g, i), (e, d), (b, h), (c, f), (b,a), (f,e)}
5. Evaluate the expression. Do not rewrite the expressions in a different form. Show each step of the calculation.
÷-×-9 5 6 × 8 4 + 1 - 2 7 (This expression is written in Polish notation).