For this case, the first thing you should do is define variables:
x = number of balls that contains the square.
On the one hand, we have:
left side: square + 6 balls
On the other hand:
right side: 10 balls
We then have to balance:
x + 6 = 10
Clearing x we have:
x = 10-6
x = 4
Answer:
a linear equation that represents the model is:
4) x + 6 = 10; x = 4