An isosceles triangle has two sides of equal length, a, and a base, b. the perimeter of the triangle is 15.7 inches, so the equation to solve is 2a + b = 15.7. which lengths make sense for possible values of b? check all that apply.
answer but which ones
–2 in.
0 in.
0.5 in.
2 in.
7.9 in.

Below is the solution:

2a + b = 15.7
b = -2a + 15.7 

These are important restrictions:0<02a + 15.7 < 15.7 

and you can solve this for a. 
Corresponding to the set of max and min for a, find b. 

See among the choices that two of them make no sense at all.
I leave actually answering the question to you; I just gave partial steps and guidance.