Well, we know the angle between the longer members is 10 degrees, because of the angles of the members to the horizontal.
We also know the larger acute angle in the triangle is 70 degrees; this too comes from the given information.
This the obstuse angle is 180 - 70 - 10 = 100 degrees.
By the law of sines, 1.4/(sin 10) = (strut)/(sin 70) = (tie bar)/(sin 100)
Thus, the tie bar is about 7.940 m long, and the strut is about 7.576 m long.