Yo please help i have no idea how to do this(the first 2 questions the tecaher did)

Step-by-step explanation:

You'll need to learn the formula for the circumference of a circle.  If the radius is r, the circumference C is C = 2πr.  It appears that your teacher is using pi for the exact circumference and 3.14 for the approximate circumference.

The radius of the first circle is 5 in.  Thus, the exact circumference is

C = 2πr = 2π(5 in) = 10π in, and the approximate circumference is

C = 2(3.14)(5 in) = 31.4 in

problem:

f(x) = - 2/3x + 5; f(5/2)

substitute 5/2 in for x:

f(5/2) = -2/3(5/2) + 5

simplify the right side:

f(5/2) = -5/3 + 5

f(5/2) = 10/3

f(5/2) = 10/3

i hope this !