3.

 The table below shows the experimental values of two variables, x and y.

 

x	-5.0	-2.5	-0.5	0.5	1.0	1.5
y	1.0	0	-8.0	12.0	7.0	5.3

  It is known that x and y are connected by . Plot against for the

 given data, and use your graph to estimate the values of a and b. Hence, or

 otherwise, find the value of y when x = 3.