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The Saussy Lumber Company ships pine flooring to three building$-$supply houses from its mills in Pineville, Oak Ridge, and Maple$-$town. Determine the best transportation schedule for the data given in the table.

$\backslash$table$[[$FROM$,\backslash$table$[[$SUPPLY$],[$HOUSE $1]],\backslash$table$[[$SUPPLY$],[$HOUSE $2]],\backslash$table$[[$SUPPLY$],[$HOUSE $3]],\backslash$table$[[$MILL$],[$CAPACITY $($TONS$)]]],[$PINEVILLE$,$$$3,$$$3,$$$2,25],[$OAK RIDGE,$$4,$$$2,$$$3,40],[$MAPLETOWN$,$$$3,$$$2,$$$3,30],[$SUPPLY$-$HOUSE DEMAND,$30,30,35,]]$

Let $P_1,P_2,$ and $P_3=$ the number of units shipped from Pineville to Supply House $1,2,$ and $3$ respectively. Let $R_1,R_2,$ and $R_3=$ the number of units shipped from Oak Ridge to Supply House $1,2,$ and $3$ respectively. Let $M_1,M_2,$ and $M_3=$ the number of units shipped from Maple$-$town to Supply House $1,2,$ and $3$ respectively.

What is the supply constraint for Supply House $2?$

a$.P_2+R_2+M_2=30$

b$.P_1+R_1+M_1=30$