iif(Transform1.posX>0,Expression1.n1+Transform1.posX*3,Expression1.n1)
Transform1.posX>0 meaning if poxX is greater than 0 (True)

then
Expression1.n1+Transform1.posX*3 (This will work)
n1 value is 1 and posX value is taken from the ball

else ball size Expression1.n1
is as ball size remain as n1