Question 179269
1.find the length of the second base (a) of a trapezoid with area A=14 units height h=4 units and base b=4.5 units? 
{{{A=(a+b/2)*h}}} multiply both sides by 2/h
{{{2A/h=a+b}}} subtract b
{{{2A/h-b=a}}} 
substitute for A, h, and b
{{{a=2*14/4-4.5}}}
a=2.5
2.Find the height (h) of a triangle with area A= 12 square units and base a=3 units?
A=1/2*a*h   multiply both sides by 2/a
h=2A/a
h=2*12/3
h=8
3.find the perimeter (P) of an equilateral rectangle with area A=1/16 square units?
Equilateral means that all the sides are equal. Therefore, an equilateral rectangle is a square. 
A=a^2
a=sqrtA
a=sqrt(1/16)
a=1/4
P=4a
P=4*1/4
P=1
4.Find the area (A)of a circle with circumference c=8 pi units?
c=d*pi
d=c/pi
d=8*pi/pi
d=8  diameter,  d=2r, r-radius
A=pi*r^2=1/4*pi*d^2
A=1/4*pi*8^2
A=16*pi