How do i solve this because i don’t know where to start

Plz hurry evaluate the expression a+b where a=8 and b=19

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

Solve for x. −3/4(x+2)=6 enter your answer in the box