i ) Power Set : {{}, {9}, {11}, {9, 11}} ii )Power Set: {{}, {+}, {-}, {×}, {÷}, {+, -}, {+, ×}, {+, ÷}, {-, ×}, {-, ÷}, {×, ÷}, {+, -, ×}, {+, -, ÷}, {-, ×, ÷}, {+, ×, ÷}, {+, -, ×, ÷}} iii ) Power Set : { φ , { φ }} iv ) Power Set : {{}, {a},{a, b },{a, {b, c}}}