2*(-1)(t+7)+(-3)*3*2+1*t*5-(1*(-1)*(-3)+(-2)*2*5+3*t*(t+7))=2*(-1)(t+7)+18+5t-(3-20+3*t*(t+7))=-2t-14+18+5t+17-3t(t+7)=-2t+4+5t+17-3t^2  
-21t=-3t^2-18t+21=-3(t^2+6t-7)