So lets look at it this way
2 numbers: x and y
and they both equal 151
sooo
x + y = 151
but we know that one is bigger by 21
sooo
x - 21 = y
And now we plug x - 21 for y
x + x - 21 = 151
No group the x's together
and our equation look like this
2x - 21 = 151 add 21 to both sides.
+21 = +21 the left side of the equal side is canceled out and we solve
************** on the right side
2x = 172 now divide both sides by 2
÷2 = ÷2 it cancels out on the left side, and we solve on the right side
so we end up with
x = 86
Now remember this from the beginning?
x - 21 = y
Well we plug in x with 86
86 - 21 = y
y = 65
So
x = 86
y = 65
and if you want to check your answer
just add them together to see if they add up to be 151
86 + 65 = 151
So the answer is correct :)
with love, the Pineapple
<3