Ihave no idea how to do this equation,

Put in the given numbers and you have two equations in two unknowns.
.. 10Ta +25Tb = 220
.. Ta +Tb = 10

It is convenient to solve this by substitution. Use the second equation to write an expression for Tb.
.. Tb = 10 -Ta
Now use this in the first equation.
.. 10Ta +25(10 -Ta) = 220
.. -15Ta +250 = 220 . . . . . . . collect terms
.. -15Ta = -30 . . . . . . . . . . . . . subtract 250
.. Ta = 2 . . . . . . . . . . . . . . . . . divide by the coefficient of Ta
.. Tb = 10 -2 = 8

Selection C is appropriate.

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