59.4cm
Use Pythagorean theorem to find the diagonal (^ means exponent)
a^2 + b^2 = c^2
42^2 + 42^2= c^2
1764+1764=c^2
3528=c^2
square root both sides
c= 59.39696962
round and you get 59.4 cm
Quick Answer SSS
Proof
AC = DB
AB = DC
BC = BC This side is equal to itself and is common to both triangles.
Three sides of one triangle equal to 3 sides of the other means that the triangles are congruent. It is the Theorem you need.
8 stamps. Multiply 2/3 by 12 and you have your answer
All u do is put 9.79 multiplied by .07 and it gives you 0.6853 so its .68 or .69 cents if u round
Is that the full question? I can't solve it if s is a variable