Hey! So with geometry, a dilation means to make something bigger(I like to think of when you go to the eye-doctor to get your eyes dilated; they get bigger so the doctor can see). Similar thing here! What we will do is simply multiply the values that are to the left of the blank triangle, then place them accordingly on the blank triangle.
Also, the 3,4,5 triangle is a special triangle which can be helpful to note in some cases.
From t'-o' the new triangle value will be 9: 3 x 3.
From t'-y' the new triangle value is 12: 4 x 3.
From o-y the new triangle value is 15: 5 x 3.
If you notice the trend, you'll see that this new dilated triangle creates another special triangle; the 9,12,15!
Here is what the new triangle should look like below :).
Hope this helps!