Micro economics

Refer :

https://www.tutorhelpdesk.com/homeworkhelp/Economics-/Perfect-Substitutes-And-Complementary-Goods-Assignment-Help.html

and
https://www.transtutors.com/homework-help/business-economics/consumer-theory/perfect-substitutes-complements.aspx

Refer this site to know all about indifference curves:
https://en.wikipedia.org/wiki/Indifference_curve

I Hope this helped clear the doubt.

yup..!!
it definitely helped..!!