Let
x------> Joanna's heart rate immediately after ran the mile
we know that
[tex] (x-\frac{2}{5}*x)=60 [/tex]
[tex] \frac{3}{5} *x=60 \\\\x=\frac{60*5}{3} \\ \\x=100\ beats\ per\ minute [/tex]
therefore
the answer is
[tex] 100\ beats\ per\ minute [/tex]