import sys

inputs = sys.stdin.readline

"""再帰関数のときセット
sys.setrecursionlimit(10**7)
import pypyjit
pypyjit.set_param('max_unroll_recursion=-1')
"""


def main():
    T = int(inputs())
    for _ in range(T):
        L, R, A, B = map(int, inputs().split())
        ans = -1 << 70
        for x in range(L, R + 1):
            val = A * x + B
            ans = max(ans, val)
        print(ans)


if __name__ == '__main__':
    main()