In △NRT,
NR=NT
∠NRT=∠NTR=x (isosceles triangle property)
Sum of angles = 180
∠NRT+∠NTR+∠RNT=180
x+x+70=180
2x=110
x=55∘
Hence, ∠NRT=55∘
In △MNS,
MN=NS (Given, NR = NT and MR = ST)
∠S=∠M=y (isosceles triangle property)
Sum of angles = 180
∠S+∠M+∠N=180
y+y+70=180
2y=110
y=55∘
Hence, ∠S=55∘