First task: To determine this we need to make difference between system that doesn't have solution and system that has infinite number of solution. If when solving equations we get 0 = 0 that means system has infinite number of equations. If we get 0 = some number that means that system doesn't have solution.
Multiplying first equation of second system by 2 and adding it to second equation we get 0=0 which means that this system has infinite number of solutions.
Answer is second system
Second task: For this we need to set a system of equations and solve it. System looks like this: x + y = 224 x*12 + y*8=2520 ------------------------- x represents older than 18 and "y" 18 and younger than that. first equation we multiply with -12 and sum it with second. -4y = -168 y=168/4 = 42
