As per given in above equation we can say
[tex]\vec a + \vec b + \vec c = 0[/tex]
so in X direction
[tex]a cos 45.4 = b cos28.2[/tex]
[tex]a = 1.255 b[/tex]
in Y direction
[tex]a sin45.4 + b sin28.2 = 25.8[/tex]
[tex]1.255 b * 0.712 + 0.472 *b = 25.8[/tex]
[tex]b = 18.9 m[/tex]
also now for a we have
[tex]a = 1.255 * 18.9 = 23.7 m[/tex]