People are different, and answering your questions can't give you an accurate quantity. Generally speaking, if your quantity is acceptable, each group is more than 20, and at least five groups are made.

At the same time, you can put your feet on a higher object, or widen the distance between two songs to increase the difficulty.

If the strength is not reached, it is necessary to define a relatively low quantity and complete it in more than 4 groups. Grouping is to fully stimulate your muscles. Push-ups mainly practice chest muscles and triceps. I suggest you practice these two parts together with the flexion and extension of the parallel bars, and the horizontal bar is also a good choice. Contact your back and arms to find a selected fitness area.