(a) E(X1 + X2 + ... + X7) = E(X1) + E(X2) + ..... + E(X7).

Var(X1 + X2 + ... + X7) = Var(X1) + Var(X2) + ..... + Var(X7) since the X's are independent

(b) It is well known that X(1) = min(X1 , X2 , ..., X7 ) has an exponential distribution with parameter (see Exponential distribution - Wikipedia, the free encyclopedia). Use this pdf to calculate Pr(X(1) > 0.33).

(c) What definition/type of kurtosis are you using?