50 + r = 3r + 20
Rearrange on either sides so it is easy to isolate
50 - 20 = 3r - r
30 = 2r
Divide by 2 to isolate r and to find its value
\(\frac{30}{2}\) = \(\frac{2r}{2}\)
2 and 2 cancels out
15 = r
Check, if you want :)
50 + (15) = 3(15) + 20
65 = 45 + 20
65 = 65
