Twice a number increased by 12 is equal to 31 less than three times the number

Measures of the angle of r, 31 s (x+4) t (3x+9)

The two square pyramids are similar. find the total volume of both pyramids if the ratio of their surface areas is 9/16

When you have 25 numbers, and jake picks 3 random numbers and puts them back, what is the chance bob has of picking those 3 numbers when he picks 6 random numbers (without putting them back)? explain.