A 45-year-old man participates in a research study investigating compensatory renal hemodynamics. He has a 7-mm stone completely obstructing his right ureter that was discovered three weeks ago. The research team uses micropuncture techniques to measure pressures in the LEFT (unobstructed) kidney, which has undergone compensatory hyperfiltration. At the afferent arteriole end of a glomerular capillary, the following values are obtained: glomerular capillary hydrostatic pressure is 55 mmHg, glomerular capillary oncotic pressure is 28 mmHg, Bowman's space hydrostatic pressure is 10 mmHg, and Bowman's space oncotic pressure is 0 mmHg. For comparison, normal glomerular capillary hydrostatic pressure is approximately 45 mmHg. The filtrate is protein-free.
Which of the following is the net filtration pressure in the unobstructed kidney?