X-78=87+12

To solve the equation \( X - 78 = 87 + 12 \), first simplify the right side:

\[ 87 + 12 = 99 \]

Now the equation is:

\[ X - 78 = 99 \]

Next, add 78 to both sides to isolate \( X \):

\[ X = 99 + 78 \]

Now, calculate \( 99 + 78 \):

\[ 99 + 78 = 177 \]

So, the solution is:

\[ X = 177 \]