Evaluating Expressions

 $3x^3-8y^2$  
if x=2 and y=-3

 $\left|a-4b\right|$  
if a=7 and b=2

 $w^2+2xy$  
if x=-3, w=-2, and y=1

 $\frac{7c^2+5}{4a-b}$  
if a=1, b=-5, and c=-4