48 because that's what you get following your equation in PEMDAS order :)
F1 . . . 100% of it = 900N is in the +x direction.
F2 . . . 70.7% of it (cos45°, 530.3N) is in the +x direction,
and 70.7% of it (sin45°, 530.3N) is in the +y direction.
F3 . . . 80% of it (520N) is in the -x direction,
and 60% of it (390N) is in the +y direction.
Total x-component: 900 + 530.3 - 520 = 1,950.3 N
Total y-component: 530.3 + 390 = 920.3 N
Magnitude of the resultant = √ (x² + y²)
= √(1950.3² + 920.3²)
= √4,650,070.09
= 2,156.4 N .
Angle of the resultant, measured counterclockwise
from the +x axis, is
tan⁻¹ (y / x)
= tan⁻¹ (920.3 / 1950.3)
= tan⁻¹ (0.4719)
= about 25.3° .
Caution:
The same fatigue that degrades my ability to READ the question accurately
may also compromise the accuracy of my solutions. Before you use this
answer for anything, check it, check it, check it !
The axis of symmetry of a parabola in the form

is a vertical line

where k is the x coordinate of the vertex of the parabola.
The x coordinate of the vertex of the parabola is given by

which in your case is

So, the axis of symmetry is the line x=12.