This is not a Normal Distribution question. Prob on each mass point is 1/18.

a)Just sum (-7)+(-6)+....+9+10 and divide by 18 to get the expectation.

Find {2(1+4+9+16+25+36+49)+64+81+100}/18. Subtract square of the expectation from this ans to get variance.

b)3/18, since here only 3 values of x=8,9,10 satisfiy x>7.

c)3