I believe the answer is 5. Hope this was right for you.
-5 (2u+10)=2 (u_7) apply distributive property
-10u-50=2u-14 collect like terms
-10u-2u=50-14 when you move the number to the other side sign change
-12u =36 to get rid of 12 divide 12 on both sides
-12u/-12= 36/-12
U= -3
1 cm = 3 m
so 5 cm = 3x5= 15 m
the actual tree is 15 m tall
