Answer:
Four covalent bonds.
Explanation:
Hello,
In this case, given the attached picture in which you can find the Lewis dot structure for metanal (formaldehyde) we can see two C-H bonds and two C-O bonds via a double bond, thus, we can compute the type of each bond given the electronegativities of hydrogen, carbon and oxygen which are 2.1, 2.5 and 3.5 respectively:

Thus, since both electronegativity difference are less 1.7 we infer that all of them are covalent, therefore, it has four covalent bonds, two C-H bonds and a double C-O bond.
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Answer:
substitution is the best method or collecting like terms
Explanation:
Period are going left to right across the periodic table
Groups are going up to down on the periodic table
Answer:
2x+3y=-6
4x+3y=12
3x-y=5
5x+3y=1
Explanation:
standard form: ax + by = C