Omg can you see the whole description of my answer? For some reason my phone is only showing "Your part one wrong" when I definitely typed more than that :( hmu if you need explanations okay? :)


Edit: I'll just explain here anyway :/
So yeah I used 161-49=112 to find the total surface area of the triangular faces of the pyramid only. I divide by four because there's a total of four triangular faces, so one triangular face is equals to 28. Apply formula of finding surface area of triangle, by making it into an equation - the slant height is the unknown here so work it out, you'll find the value of the unknown (the slant height.
For part two, i made the height of pyramid unknown first, then I applied Pythagoras theorem to find this height. Apply formula to find volume of pyramid and that's how you get the answer.