First, find the slope.
m = (y2 - y1) / (x2 - x1)
m = (7 - 2/3) / (4/5 - 3/8)
m = (21/3 - 2/3) / (32/40 - 15/40)
m = (19/3) / (17/40)
m = (19/3) * (40/17)
m = (19*40) / (3*7)
m = 780 / 21
m = 260 / 7
Now point-slope form:
y - y1 = m(x - x1)
y - 7 = (260/7)(x - 4/5)
y - 7 = (260/7)x -(260/7)(4/5)
y - 7 = (260/7)x - (52/7)(4/1)
y - 7 = (260/7)x - 208/7
y = (260/7)x - 208/7 + 7
y = (260/7)x - 208/7 + 49/7
y = (260/7)x - 159/7