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Question

On a parkinglot there is X cars and there is Y motorcycles. It is 25 vehicles all together. The the vehicles has 90 wheels all together.

Answer 1

What have you tried?

Answer 2

   x + y = 25
    4x + 2y = 90
    4*(25 - y) + 2y = 90

From there, you can guess Y:

    100 - 4y + 2y = 90
    100 - 2y = 90
    -2y = -10
    y = 5

From there you can guess X:

    x + 5 = 25
    x = 20