Please help me with this maths problem cant understand how to work it out

[dominatrix1]

baisically i am trying to work out point elasticity of demand, where formula is dD/dP x p/d
the bit i am stck on in this question is multiiplying (p-5)^2 * (50+200/p-5) , the answer should be 50(p-5)(p-1) can someone explain to mee how this works

 

[AGD]

(p-5)^2*(50+200/(p-5))=

=(p-5)^2* (50(p-5)+200)/(p-5)

=(p-5)(50p-250+200)

=(p-5)*50*(p-1)