A bank gives each customer a 4-digit code. The code number is assigned randomly from the digits 1, 3, 5, and 7, and no digit is repeated. How many code combinations are possible?

step-by-step explanation:

step 1: solve one of the equations for one of the variables. let's solve the first equation for y:

step 2: substitute that equation into the other equation, and solve for x.

step 3: substitute x = 4 x = 4 x=4 into one of the original equations, and solve for y.

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step-by-step explanation: