var frogs = parseInt(readline());
var t = [];
var x = [];

var a = 0, b = 0, k = 0;
var result;

for (var i = 0; i < frogs; i++)
{
    t = readline().split(' ');
    a = parseInt(t[0]);
    b = parseInt(t[1]);
    k = parseInt(t[2]);

    result = a * parseInt(k / 2 + k % 2) - b * parseInt(k / 2);
    x.push(result);

}
for ( var i = 0; i < x.length; i++)
{
    print(x[i]);
}