You want the saturated vapour pressure,
P
SVP
.
Explanation:
This is a function of temperature only, and at
283
⋅
K
this site reports that the vapour pressure of water,
P
SVP
, is
9.2
⋅
m
m
⋅
H
g
.
And so,
P
Measured
=
P
gas
+
P
SVP
,
P
Gas
=
P
Measured
−
P
SVP
750
⋅
m
m
⋅
H
g
−
9.2
⋅
m
m
⋅
H
g
=
741.8
