Idon't understand this i posted both answer choice and question

Which expression gives the area of the triangle shown below

Ijust need to see how to do this. so you don’t have to answer all of them just a step by step explanation of one.

Serena is making an experiment. for that, she needs 20 grams of a 52% solution of salt. she has two large bottles of salt water: one with 40% and the other with 70% of salt in them. how much of each must she use to make the solution she needs? i am in need of