#### Answer

$(12.99x-16.2y)$ m/s

#### Work Step by Step

vec(A)=$5x$ m/s
vec(B)=$10cos60^{\circ}x+10sin60^{\circ}y=5x+8.7y$ m/s
vec(C)=$-15cos30^{\circ}+15sin30^{\circ}y=-12.99x+7.5y$ m/s
So,
vec(A)-vec(B)-vec(C)= $5x-5x-8.7y+12.99x-7.5y$ m/s
= $(12.99x-16.2y)$ m/s