Answer:
Value of x is used to consider unknown value. The letter “x” is commonly used in algebra to indicate an unknown value. It is referred to as a “variable” or, in some cases, a “unknown.” In x + 2 = 7, x is a variable. ... A variable need not be “x,” but might be “y,” "w," or any other letter, name, or symbol.
The equation of any straight line, called a linear equation, can be written as: y= mx+b, where my is the slope of the line and b is the y-intercept. The y-intercept of this line is the value of y at the point where the lone crosses the y axis.

Actually Welcome to the Concept of the Functions.
Let's first find the g(-1),
so we get as
3(-1)^2 +5(-1)-6
=> 3 -5-6
=> -8
now since g(-1) =-8
let's find f(g(-1)) that is f(-8)
f(-8) = 4(-8) + 14
=> f(g(-1)) = -32+14
=> f(g(-1)) = -18
-18 is the answer.