U gotta use pythagorean theory
So a^2 +b^2 = c^2
C=7 since its the one facing the right angle
5.2^2 + b^2 = c2
27.04 +b^2= 49
Subtract 21.96 from both sides, so ur left with 21.96=b^2
Under the square root and rounded up would equal 4.7
Hope this helps