Very good with those two equations.

Now solve those simultaneously.

You don't want to know the T, so eliminate T either by substitution or by division.

By substitution;

From the first equation,

T = 190 /(315 +x)

Substitute that into the second equation,

(315 -x)*[190 /(315 +x)] = 125

190(315 -x) = 125(315 +x) ------**

Maybe you can continue from there.

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By division:

Divide the first equation by the second equation,

(315 +x) /(315 -x) = 190 /125

Cross multiply,

125(315 +x) = 190(315 -x) -----same as the above.