pay back period

hi 1) so if a question is asking me for payback period, do i use the discounted pay back or the one with cashflows that have not been discounted 2) one of the question in the practice tests asked me to calculate total cost but it did not specify if its total cost using absorption or marginal, how do i go about it 3)Question, a company uses standard marginal costing. last month the standard contribution on actual sales was 10 000 and the following variances arose i.total variable costs variance 2000adv ii.sales price variance 500fav iii.sales volume variance 1000adv what is the actual contribution for the month? please help be answer this question and explain to me the variances that i take account of and why. sorry this is pretty lengthy