If a=3 and b=5 , what is the value of ? a^2+b^2

Solve the equation for x.3(6x - 1) = 12 i've tried doing the math and i can't find out what i'm doing wrong

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?

The length of a rectangle plus its width is 24 cm. the area is 143 square cm. what are the length and width of the rectangle?