Verified answer

[tex]\displaystyle\bf\\-7d(7d+7)+(7d-7)(7+7d)=-49d^{2} -49d+(7d)^{2} -7^{2}=\\\\=-49d^{2} -49d+49d^{2} -49=-49d-49=-49(d+1)\\\\d=6,2\\\\-49(d+1)=-49\cdot(6,2+1)=-49\cdot 7,2=-352,8\\\\Otvet: \ -352,8[/tex]