Walls by a Nut and Washer $\left( d _ { w } = 22 \mathrm {~mm} \right)$

$\text { A threaded steel rod } \left( E _ { s } = 210 \mathrm { GPa } , d _ { r } = 15 \mathrm {~mm} \text {, cte } e _ { s } = 12 \times 10 ^ { - 6 / { } ^ { \circ } \mathrm { C } } \right) \text { is held stress-free between rigid }$ walls by a nut and washer $\left( d _ { w } = 22 \mathrm {~mm} \right)$ assembly at each end. If the allowable bearing stress between the washer and wall is $55 \mathrm { MPa }$ and the allowable normal stress in the rod is $90 \mathrm { MPa }$ , the maximum permissible temperature drop $\Delta T$ is approximately:

A) $25 ^ { \circ } \mathrm { C }$
B) $30 ^ { \circ } \mathrm { C }$
C) $38 ^ { \circ } \mathrm { C }$
D) $46 ^ { \circ } \mathrm { C }$