400
(m+3)/8 = 40/64
What is m=2?
Reason: When solving proportions, you have to cross-multiply. So, you multiply (m+3) and 64 to get 64m+ 192, and you multiply 8 and 40 to get 320. So, 64m+192=320. Now, you solve like you would if it was a two-step problem because essentially, it is. You subtract 192 from both sides, to get 128. Finally, you divide bot sides by 64 to get 2.