Triangles are similar and only differ in size meaning they are dilated
So first we have to find the scale factor of dilation (by how much the smaller triangle got bigger)
Find scale factor:
2.4a=4.8
z=2
Find x:
we multiply the original side of the small side with the scale factor of 2
2.8(2)=x
5.6=x
So, x=5.6