The difference between twice a number and half the number is 30. What is the number

Tim's phone service charges $26.39 plus an additional $0.21 for each text message sent per month. if tim's phone bill was $31.64, which equation could be used to find how many text messages, x, tim sent last month?

Emily is entering a bicycle race for charity. her mother pledges $0.90 for every 0.75 mile she bikes. if emily bikes 18 miles, how much will her mother donate?

6cm10 cma conical paper cup has dimensions as shown in the diagram. how much water can the cup hold when full?