Can anyone ? give the answer in four significant figures.

X + 0.5y = 3
x^2 - y = 15

from the first equation:-
0.5y = 3 - x
y = 6 - 2x

Substitute for y in second equation:-
x^2 - (6 - 2x) = 15
x^2 + 2x - 21 = 0
x  =  [-2 +/- sqrt((4 - 4*-21)] / 2
    = 3.6904 ,  -5.6904

Plugging in these into  first equation we get

3.6904 + 0.5y = 3  so y = 2(3-3.6904) =  -1.3808
-5.6904 + 0.5y = 3 so y = 2(3 + 5.6904) =  17.3808

Solution is  x = 3.690, y = -1.381  ;   x = -5.690, y = 17.38 ( to 4 s.f's)

It’s hard to understand what you put.. can you show a picture ?