Ok so first u have to devide the 51 into 4. So 51 divided by 4 is 12.75. Then it is 75% of it so 75% is 3/4 so you will have to multiply 12.75 by 3. That would equal 38.25. YOUR ANSWER IS 38.25
For this case what you should do is evaluate values of x in the function and verify that they meet the result of f (x) shown in the graph.
The answer is
f (x) = - 2lxl +1
notice that
f (1) = - 2l1l + 1 = -1
f (-1) = - 2l-1l + 1 = -1
Both comply with the value of f (x) shown in the graph
answer
f (x) = - 2lxl +1