Can some one explain how to get the answer and what is the answer

If 30 lb of rice and 30 lb of potatoes cost ? $27.60? , and 20 lb of rice and 12 lb of potatoes cost ? $15.04? , how much will 10 lb of rice and 50 lb of potatoes? cost?

Tessa bought stock in a restaurant for $253.00. her stock is now worth $333.96. what is the percentage increase of the value of tessa's stock? a.) 81% b.) 32% c.) 24% d.) 76%

Aclassroom is made up of 11 boys and 14 girls. the teacher has four main classroom responsibilities that she wants to hand out to four different students (one for each of the four students). if the teacher chooses 4 of the students at random, then what is the probability that the four students chosen to complete the responsibilities will be all boys?