the circumference of a circle varies directly as the radius if the circumference is 18 cm when the radius is 3

The brain volumes (cm cubed) of 50 brains vary from a low of 904 cm cubed to a high of 1488 cm cubed. use the range rule of thumb to estimate the standard deviation s and compare the result to the exact standard deviation of 175.5 cm cubed, assuming the estimate is accurate if it is within 15 cm cubed

Geometry in the diagram, ∠abc is a right angle. ∠dbc = 30°27'40". find the measure of ∠abd.

Does anyone know how to solve and graph this: 4 + | a + 2 | < 7the only part i don't get is the "4 +"