Fill data in one cell from another based on criteria from a third

I'm trying to figure out which function, if any, would be best to use to pull data from one cell (column B) based on a value of an associated cell (column A) and fill it into a third cell.

m/z Intensity Relative

35.5 703 1.1
36.3 780 1.23
37.2 4119 6.47
38.2 3952 6.21 m/z abundance
39.2 1961 3.08 50
40.3 743 1.17 75
41.4 243 0.38 95
42.1 235 0.37 96
43.3 362 0.57 173
44.2 1535 2.41 174
45.3 683 1.07 175
46.4 464 0.73 176
47.3 443 0.7 177
48.1 479 0.75
49.1 2976 4.67
50.1 13768 21.63
51.2 4268 6.7
52.2 435 0.68
53.3 146 0.23
54.6 323 0.51
55.3 316 0.5
56.2 1352 2.12
57.2 2497 3.92
58.2 145 0.23
59 176 0.28


In this instance I want to automatically fill the abundance column based on a lookup of the values in the m/z column. For the m/z 50, find the correct m/z in column a and copy the corresponding abundance from column B into the empty abundance position. I was guessing an If statement, but wasn't sure of the arguments for the statement.