help please 4-6

4. The summation of integers ni can be represented by the following sum function Sum(n)=1+2+3+n Which of the following will be the value of Sum (n)? a. n(n+1) b. (1/2)(n)+(1/2)n n n2 means n to the power 2} c. (n+1)(n+2) d. (1/2)(2n+1)(2n+3) e. None of the above 5. Consider the ADT Stack of integers. If a sequence of integers, 10, 2030,40,50 are pushed on the stack, what will the print-out of the stack be? a. 1020304050 b. 2030405010 c. 5040302010 d. 5030402010 e. none of the above 6. Consider the ADT Stack of integers. If a sequence of integers, 10, 2030,40,50 are pushed on the stack and the pop operation is performed two times, what will the print-out of the stack be? a. 102030 b. 203040 c. 302010 d. 304020 e. none of the above