Let x represent the smaller. Then x+1 is the greater of the two.
... x+1 = 2x +20
... 0 = x + 19 . . . . . subtract x+1
... x = -19
Your two integers are -19 and -18.
let's say the bill without the tip is "x" amount, so that'd be the 100% of the bill, but we also know that 4.50 is the 18% of "x".
so if 4.50 is the 18% of "x", how much is "x"?

Answer:
A triangle equals 180 degrees.
Copper: Nickel = 4:1
a) How much copper needed for 20 kg nickel
C:N = 4: 1
C:20 = 4:1
C/20 = 4/1 Cross Multiply
C*1 = 4*20
C = 80
80kg Copper would be needed.
b) How much Nickel would be needed for 20 kg of Copper
C:N = 4: 1
20:N = 4:1
20/N = 4/1 Cross Multiply
4*N = 1*20
4N = 20 Divide both sides by N.
N = 20/4 = 5
5kg Nickel would be needed.