Can someone me with these questions?

#3 can and #4 cannot form a triangle.

Why? For a triangle to be formed, two shortest lengths of a triangle must be greater than the longest length, or else all three lengths cannot connect. It makes most sense when you visualize it.

For #3, 1/4 + 1/3 > 1/2

For #4, .01 + .02 < .205, therefore cannot form a triangle.