1077A - Frog Jumping - CodeForces Solution

t = int(input())
sum1 = 0
sum2 = 0

for i in range(t):
    a, b, k = map(int, input().split())
    sum1 = int(a * (k // 2))
    sum2 = int(b * (k // 2))
        
    if k % 2 == 1:
        sum1 = sum1 + a
        
    print(sum1 - sum2)
    sum1 = 0
    sum2 = 0