Can anybody help provide the steps?

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

Prove that 16^4-2^13-4^5 is divisible by 11.

How are algebraic expressions evaluated using substitution?