Answer
$17^{\circ}$
Work Step by Step
m$\angle$TSW = m$\angle$TSU + m$\angle$USV + m$\angle$VSW
m$\angle$TSW = (m$\angle$TSW - m$\angle$USW) + m$\angle$USV + (m$\angle$TSW - m$\angle$TSV)
61 = (61 - 40) + m$\angle$USV + (61 - 38)
61 = 122 - 78 + m$\angle$USV
61 = 44 + m$\angle$USV
m$\angle$USV = $17^{\circ}$
