t = int(input())
for lp in range(t):
    #print(f"Now loop: {lp}")
    l,r,a,b = map(int,input().split())
    g = None
    for i in range(l,r+1):
        f = i*a+b
        if g==None:
            g = f
        if f > g:
            g = f
    print(g)