prisma segitiga. panjang rusuk alas 4 cm dan tinggi prisma 7 cm maka luas bidang tegak prisma adalah... bantuin saya guys

L = 2.La.Ka.t
=2.(Lsegitiga.a+Ksegitiga.t).t
=2.(a.t/2.t+4.7.7).t
=2.(4.7/2.4+199.7
=2.28.2+196.7
=46.2+196.7
=92+196.7
=288.7
=2016 cm